High Fidelity Restriction Endonucleases

ABSTRACT

Methods and compositions are provided for engineering mutant enzymes with reduced star activity where the mutant enzymes have a fidelity index (FI) in a specified buffer that is greater than the FI of the non-mutated enzyme in the same buffer.

CROSS REFERENCE

This is a divisional of U.S. patent application Ser. No. 13/022,561, filed Feb. 7, 2011, which is a continuation-in-part of U.S. patent application Ser. No. 12/172,963 filed Jul. 14, 2008, herein incorporated by reference. This application also claims priority from U.S. provisional application Ser. No. 60/959,203 filed Jul. 12, 2007, Ser. No. 61/301,666 filed Feb. 5, 2010, and Ser. No. 61/387,800 filed Sep. 29, 2010, herein incorporated by reference.

BACKGROUND

Restriction endonucleases are enzymes that cleave double-stranded DNAs in a sequence-specific manner (Roberts, R. J. Proc Natl Acad Sci USA 102: 5905-5908 (2005); Roberts, et al. Nucleic Acids Res 31:1805-1812 (2003); Roberts, et al. Nucleic Acids Res 33:D230-232 (2005); Alves, et al. Restriction Endonucleases, “Protein Engineering of Restriction Enzymes,” ed. Pingoud, Springer-Verlag Berlin Heidelberg, New York, 393-407 (2004)). They are ubiquitously present among prokaryotic organisms (Raleigh, et al., Bacterial Genomes Physical Structure and Analysis, Ch.8, eds. De Bruijin, et al., Chapman & Hall, New York, 78-92 (1998)) in which they form part of restriction-modification systems, which mainly consist of an endonuclease and a methyltransferase. The cognate methyltransferase methylates the same specific sequence that its paired endonuclease recognizes and renders the modified DNA resistant to cleavage by the endonuclease so that the host DNA can be properly protected. However, when there is an invasion of foreign DNA, in particular bacteriophage DNA, the foreign DNA will be degraded before it can be completely methylated. The major biological function of the restriction modification system is to protect the host from bacteriophage infection (Arber Science 205:361-365 (1979)). Other functions have also been suggested, such as involvement in recombination and transposition (Carlson, et al. Mol Microbiol, 27:671-676 (1998); Heitman, Genet Eng (NY) 15:57-108 (1993); McKane, et al. Genetics 139:35-43 (1995)).

The specificity of the approximately 3,000 known restriction endonucleases for their greater than 250 different target sequences could be considered their most interesting characteristic. After the discovery of the sequence-specific nature of the first restriction endonuclease (Danna, et al., Proc Natl Acad Sci USA 68:2913-2917 (1971); Kelly, et al., J Mol Biol 51:393-409 (1970)), it did not take long for scientists to find that certain restriction endonucleases cleave sequences which are similar but not identical to their defined recognition is sequences under non-optimal conditions (Polisky, et al., Proc Natl Acad Sci USA, 72:3310-3314 (1975); Nasri, et al., Nucleic Acids Res 14:811-821 (1986)). This relaxed specificity is referred to as star activity of the restriction endonuclease.

Star activity is a problem in molecular biology reactions. Star activity introduces undesirable cuts in a cloning vector or other DNA. In cases such as forensic applications, where a certain DNA substrate needs to be cleaved by a restriction endonuclease to generate a unique fingerprint, star activity will alter a cleavage pattern profile, thereby complicating analysis. Avoiding star activity is also critical in applications such as strand-displacement amplification (Walker, et al., Proc Natl Acad Sci USA, 89:392-396 (1992)) and serial analysis of gene expression (Velculescu, et al., Science 270:484-487 (1995)).

SUMMARY

In an embodiment of the invention, a method is provided of identifying a fidelity index (FI) of a restriction endonuclease and variants thereof that includes selecting a reaction buffer and a DNA substrate containing the binding and cleavage site of the restriction endonuclease; permitting the serially diluted restriction endonuclease or variants thereof to cleave the DNA substrate; and determining an FI for each of the restriction endonucleases and the one or more variants thereof.

In an embodiment, the method further comprises comparing the FI for the restriction endonuclease and the variants thereof to obtain an improvement factor of, for example, greater than 2 for the variant.

In an embodiment of the invention, a buffer is selected that includes potassium acetate, Tris acetate and magnesium acetate; or magnesium chloride.

Additional embodiments include:

-   -   (a) A composition, comprising: an enzyme comprising SEQ ID No. 1         in which one or more amino acids have been mutated, wherein the         position of one or more mutations is selected from the group         consisting of S36, K77, P154, E163, Y165 and K185.     -   (b) A composition, comprising: an enzyme comprising SEQ ID No. 2         in which one or more amino acids have been mutated, wherein the         position of one or more mutations is selected from the group         consisting of K198 and Q148.     -   (c) A composition, comprising: an enzyme comprising SEQ ID No. 3         in which one or more amino acids have been mutated, wherein the         position of one or more mutations is selected from the group         consisting of S15, H20, E34, M58, Q95, R106, K108, T181, R187         and R199.     -   (d) A composition, comprising: an enzyme comprising SEQ ID No. 4         in which one or more amino acids have been mutated, wherein the         position of one or more mutations is selected from D16, D148 and         E132.     -   (e) A composition, comprising: an enzyme comprising SEQ ID No. 5         in which one or more amino acids have been mutated, wherein the         position of one or more mutations is selected from the group         consisting of K75, N146 and D256.     -   (f) A composition, comprising: an enzyme comprising SEQ ID No. 6         in which one or more amino acids have been mutated, wherein the         position of one or more mutations is selected from the group         consisting of E198 and D200.     -   (g) A composition, comprising: an enzyme comprising SEQ ID No. 7         in which one or more amino acids have been mutated, wherein the         position of one or more mutations is selected from the group         consisting of K229, E025, R034 and Q261.     -   (h) A composition, comprising: an enzyme comprising SEQ ID No. 8         in which the position of the mutation is K225.     -   (i) A composition, comprising: an enzyme comprising SEQ ID No. 9         in which one or more amino acids have been mutated, wherein the         position of one or more mutations is selected from the group         consisting of H137, D177, K363, K408, R411, Q215, Q226 and Q230.     -   (j) A composition, comprising: an enzyme comprising SEQ ID No.         10 wherein the position of the mutation is F376.     -   (k) A composition, comprising: an enzyme comprising SEQ ID No.         11 in which one or more amino acids have been mutated, wherein         the position of one or more mutations is selected from the group         consisting of R78, T140, E152, R199 and F217.     -   (l) A composition, comprising: an enzyme comprising SEQ. ID No.         12 in which one or more amino acid have been mutated, wherein         the position of one or more mutations is selected from the group         consisting of G26, P105, T195, Q210, Y147, Y193, K114, T197,         S245, D252 and Y027.     -   (m) A composition, comprising: an enzyme comprising SEQ ID No.         13 in which one or more amino acids have been mutated, wherein         the position of one or more mutations is selected from the group         consisting of H10, N208, K48, K74, R75, Y56, K58 and M117.     -   (n) A composition, comprising: an enzyme comprising SEQ ID No.         14 in which one or more amino acids have been mutated, wherein         the position of one or more mutations is selected from the group         consisting of K014, Q069, E099, R105, R117, G135 and Y035.     -   (o) A composition, comprising: an enzyme comprising SEQ ID No.         15 in which one or more amino acids have been mutated, wherein         the position of one or more mutations are selected from the         group consisting of N106, Q169, E314 and R126.     -   (p) A composition, comprising: an enzyme comprising SEQ ID No.         16 in which one or more amino acids have been mutated, wherein         the position of one or more mutations is selected from the group         consisting of T20, P52, Y67, K68, R75, E86, Q90, S91, Q93, H121         and G172.     -   (q) A composition, comprising: an enzyme comprising SEQ ID No.         17 in which one or more amino acids have been mutated, wherein         the position of one or more mutations selected from the group         consisting of E059, P065, S108, N172, K174, Q179, G182 and Y055.     -   (r) A composition, comprising: an enzyme comprising SEQ ID No.         18 in which one or more amino acids have been mutated, wherein         the position of one or more mutations is selected from the group         consisting of N212 and L213.     -   (s) A composition, comprising: an enzyme comprising SEQ ID No.         19 having a mutation at position N65.     -   (t) A composition, comprising: an enzyme comprising SEQ ID No.         20 in which one or more amino acids have been mutated, wherein         the position of one or more mutations is selected from the group         consisting of E007, D011, E049, R073, R114, G137, S210 and R213.     -   (u) A composition, comprising: an enzyme comprising SEQ ID No.         21 in which one or more amino acids have been mutated, wherein         the position of one or more mutations is selected from the group         consisting of P079, E086, H096 and E218.     -   (v) A composition, comprising: an enzyme comprising SEQ ID No.         22 in which one or more amino acids have been mutated, wherein         the position of one or more mutations is selected from the group         consisting of E32, S081, G132, F60 and S61.     -   (w) A composition, comprising: an enzyme comprising SEQ ID No.         23 in which one or more amino acids have been mutated, wherein         the position of one or more mutations is selected from the group         consisting of G013, G016, K018, P052, R053, K070, E071, D072,         G073, S84, E086, R090, K094, R095, P099, P103, K113, N135, S151,         P157, G173, T204, S206, K207, E233, N235, E237, S238, D241,         K295, S301 and S302.     -   (x) A composition, comprising: an enzyme comprising SEQ ID No.         24 in which one or more amino acids have been mutated, wherein         the position of one or more mutations is selected from the group         consisting of S64, S80, S162, T77/T96 and N178.     -   (y) A composition, comprising: an enzyme comprising SEQ ID No.         25 in which the position R232 is mutated.     -   (z) A composition, comprising: an enzyme comprising SEQ ID No.         26 in which one or more amino acids have been mutated, wherein         the position of one or more mutations is selected from the group         consisting of S50, Y81, N93 and W207.     -   (aa) A composition, comprising: an enzyme comprising SEQ ID No.         27 having a mutation at G26.     -   (bb) A composition, comprising: an enzyme comprising SEQ ID No.         28 having a mutation at E112/R132.     -   (cc) A composition, comprising: an enzyme comprising SEQ ID No.         29 in which one or more amino acids have been mutated, wherein         the position of one or more mutations is selected from the group         consisting of N016, S33, P36, H76, P87, N89, R90, T138, K141,         K143, Q221, Q224, N253, Q292, R296, T152, G326 and T324.     -   (dd) A composition, comprising: an enzyme comprising SEQ ID No.         30 in which one or more amino acids have been mutated, wherein         the position of one or more mutations is selected from the group         consisting of K024, P214, E146, N251 and Y095.     -   (ee) A composition, comprising: an enzyme comprising SEQ ID No.         31 in which one or more amino acids have been mutated, wherein         the position of one or more mutations is selected from the group         consisting of G075, Q099, G155, P022 and R90.     -   (ff) A composition, comprising: an enzyme comprising SEQ ID No.         32 in which one or more amino acids have been mutated, wherein         the position of one or more mutations is selected from the group         consisting of S097 and E125.     -   (gg) A composition, comprising: an enzyme comprising SEQ ID No.         33 in which one or more amino acids have been mutated, wherein         the position of one or more mutations is selected from the group         consisting of K021, I031 and T120.     -   (hh) A composition, comprising: an enzyme comprising SEQ ID No.         34 in which one or more amino acids have been mutated, wherein         the position of one or more mutations is selected from the group         consisting of K7, T10, N11, N14, Q232 and T199.     -   (ii) A composition, comprising: an enzyme comprising SEQ ID No.         35 in which one or more amino acid have been mutated, wherein         the position of one or more mutations is selected from the group         consisting of P92, P144, G197 and M198.

Any of the above compositions may be further characterized in that the mutated enzyme has an FI in a predetermined buffer that is greater than the enzyme without the mutations in the predetermined buffer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B show the comparison of PvuI-HF and PvuI-WT activity.

In FIG. 1A, the asterisk (*) sign denotes the lane on the left (lane 2) in which star activity is no longer detected. The number (#) sign denotes the lane on the right (lane 8) in which partial digestion occurs. The starting concentration of the PvuI-WT was calculated to be 77 units.

In FIG. 1B, complete digestion was observed until lane 15, after which star activity was observed. The window of dilution allowing for complete digestion expanded from 6 dilutions to 15 dilutions in the series. The starting concentration of the PvuI-HF was calculated to be at least 9600 units.

FIGS. 2A and 2B show the comparison of HindIII-HF and HindIII-WT activity.

In FIG. 2A, the asterisk (*) sign denotes the lane on the left (lane 9) in which star activity is no longer detected. The number (#) sign denotes the lane on the right (lane 15) in which partial digestion occurs. The starting concentration of the HindIII-WT was calculated to be 9,600 units.

In FIG. 2B, complete digestion was observed until lane 13, after which star activity is observed. The window of dilution allowing for complete digestion expanded from 6 dilutions to 13 dilutions in the series. The starting concentration of the HindIII-HF was calculated to be at least 2,400 units.

FIGS. 3A and 3B show the comparison of DraIII-HF and DraIII-WT activity.

In FIG. 3A, the asterisk (*) sign denotes the lane on the left (lane 12) in which star activity is no longer detected. The number (#) sign denotes the lane on the right (lane 12) in which partial digestion occurs. Neither star activity nor partially digested DNA was observed. The starting concentration of the DraIII-WT was calculated to be 1,200 units.

In FIG. 3B, complete digestion was observed until lane 12, after which star activity is observed. The starting concentration of the DraIII-HF was calculated to be at least 1,200 units.

FIGS. 4A and 4B show the comparison of KpnI-HF and KpnI-WT activity.

In FIG. 4A, the * sign denotes the lane on the left (lane 9) in which star activity is no longer detected. The # sign denotes the lane on the right (lane 13) in which partial digestion occurs. In FIG. 1A, the starting concentration of the KpnI-WT was calculated to be 2,000 units.

In FIG. 4B, complete digestion was observed throughout with no star activity or partial digestion. The starting concentration of the KpnI-HF was calculated to be greater than 12,000 units.

FIGS. 5A-5B shows the comparison of StyI-HF and StyI-WT.

In FIG. 5A, the * sign shows the beginning of the star activity on its left (lane 6), the # sign shows the beginning of partial activity on its right (lane 12). The starting amount of Sty-WT was calculated to be 1,000 units.

In FIG. 5B, star activity was observed in the first 2 lanes and partial digestion from lane 14 or 15. The starting amount of StyI-HF was calculated to be 4,000 units.

FIG. 6 shows a comparison of BglI-HF and BglI-WT on pXba. The BglI-HF has an FI of at least 8,000 while the BglI-WT has an FI of 32, providing an improvement factor of at least 250. The right panel is the theoretical digestion pattern.

FIG. 7 shows a comparison of BsrDI-HF and BsrDI-WT on pBR322. The BsrDI-HF has an FI of at least 1,000 in NEB4, while the BsrDI-WT has an FI of ½, providing an improvement factor of at least 2,000. The right panel is the theoretical digestion pattern.

FIG. 8 shows a comparison of BclI-HF and BclI-WT in NEB4 on lambda (dam⁻). The BclI-HF has an FI of at least 2,000, while the BclI-WT has an FI of 32, providing an improvement factor of at least 64. The right panel is the theoretical digestion pattern.

FIG. 9 shows a comparison of BglII-HF and BglII-WT on pXba. The BglII-HF has an FI of at least 32,000, while the BglII-WT has an FI of 16, providing an improvement factor of at least 2,000. The right panel is the theoretical digestion pattern.

FIG. 10 shows a comparison of BstEII-HF and BstEII-WT on lambda DNA. The BstEII-HF has an FI of at least 2,000, while the BstEII-WT has an FI of 4, providing an improvement factor of at least 500. The right panel is the theoretical digestion pattern.

FIG. 11 shows a comparison of SfiI-HF and SfiI-WT on pBC4. The SfiI-HF has an FI of at least 8,000 in NEB4, while the SfiI-WT has an FI of 64, providing an improvement factor of at least 120. The right panel is the theoretical digestion pattern.

FIG. 12 shows a comparison of SmaI-HF and SmaI-WT on pXba. The SmaI-HF has an FI of at least 256,000, while the SmaI-WT has an FI of 64, providing an improvement factor of at least 4,000. The right panel is the theoretical digestion pattern.

FIG. 13 shows a comparison of BsmBI-HF and BsmBI-WT on lambda DNA. The BsmBI-HF has an FI of 250 in NEB4, while the BsmBI-WT has an FI of 4, providing an improvement factor of at least 64. The right panel is the theoretical digestion pattern.

FIG. 14 shows a comparison of BstNI-HF and BstNI-WT on pBR322. The BstNI-HF has an FI of 500 in NEB4, while the BstNI-WT has an FI of 4, providing an improvement factor of at least 120. The right panel is the theoretical digestion pattern.

FIG. 15 shows a comparison of MluI-HF and MluI-WT on lambda DNA. The MluI-HF has an FI of at least 32,000 in NEB4, while the MluI-WT has an FI of 32, providing an improvement factor of at least 1,000. The right panel is the theoretical digestion pattern.

FIG. 16 shows a comparison of NspI-HF and NspI-WT on pUC19. The NspI-HF has an FI of 500 in NEB4, while the NspI-WT has an FI of 32, providing an improvement factor of at least 16. The right panel is the theoretical digestion pattern.

FIG. 17 shows a comparison of BsrFI-HF and BsrFI-WT on pBR322. The BsrFI-HF has an FI of at least 500 in NEB4, while the BsrFI-WT has an FI of 16, providing an improvement factor of at least 32. The right panel is the theoretical digestion pattern.

DETAILED DESCRIPTION OF EMBODIMENTS

The generation of mutants of restriction endonucleases with improved specificity for a single sequence is not straightforward. Numerous problems were encountered. These include the following: a mutated enzyme had reduced or no activity, did not have reduced star activity or actually had increased star activity. Alternatively, a mutated enzyme could not be cloned and therefore could not be analyzed.

Failure to produce a mutant resulted from any of a variety of possible causes including any of the following. It could be due to failed inverted PCR. It is also possible that the mutation which generated new specific activity was toxic to a host cell even if it expressed the cognate methylase under conditions that were normally protective for expression of the non-mutated restriction endonuclease. In these circumstances, no viable mutant clone would be obtained. Alternatively, the mutant might have a preference for a particular buffer such that when tested in another buffer, no activity would be detected. Another difficulty encountered, was that although generally a crude lyzate of each mutation was tested, in some case, the enzyme had to be purified to detect activity where activity was not detected in the lysate scoring the assay negative.

It was surprising to note that in several examples, a change of a proline to an alanine resulted in variants with a desired FI of at least greater than 250 and yielding an improvement factor of at least two fold. This was exemplified in variants of PvuI, BamHI, NruI and SpeI.

Other challenges in producing high fidelity mutants include the size of the DNA encoding some restriction endonucleases. This DNA may be difficult to amplify by PCR given the large size of the template. Moreover, the PCR products in some circumstances did not readily transform into a new host. Even if a host cell transformation was successful, transformed is cells did not always produce colonies and hence could not be readily detected. In some cases, even if the colonies were obtained from transformation, they could be not cultured in any condition.

Reasons for reduction in the specific activity of mutants may result from any of the following: the mutation interferes with the folding of the protein which significantly lowered the expression level or the mutation affects the specific enzyme activity.

For example, this was observed for StyI mutants: N34A, F35A, D58A, F65A, K66A, K67A, F100A, N148A, E213A, F250A, T251A, D258A, D262A, N283A, R293A, F294A, R295A, R296A, D298A, D299A, M304A, M310A, D318A, S337A, S346A and F371A.

Loss of enzyme activity may result from causes that include any of the following: the mutation deleted the residues which are important in catalysis; or the mutations changed residues that are important in folding, thus, the misfolded mutant protein is inactive.

For example, this was observed for StyI mutants M33A, D37A, F41A, D55A, D71A, N77A, R79A, E80A, F81A, T82A, E83A, F97A, F101A, E136A, W137A, M138A, M140A, K144A, Q145A, R151A, R255A, R259A, S261A, T264A, F278A, R281A, T284A, M297A, H305A, N306A, D314A, D338A and E382A.

Generating high fidelity mutants requires painstaking work. Multiple mutants are selected and tested and only a relatively small number show high fidelity. It was not possible to predict by extrapolation which mutants are likely to show improved properties.

Examples of assays performed to identify high fidelity variants of restriction endonucleases are shown in FIGS. 1-17. The figures show the results in a single buffer for both wild type and high fidelity variants. All the figures show amounts and types of cleavage of DNA after a series of two fold dilutions from left to right on the gel with the concentration of enzyme decreasing in the direction of the triangle. Table 1 details the results for the 33 exemplified enzymes. The restriction endonuclease reaction buffers (buffers 1-4) used in the examples are defined for example in the NEB catalog (2009/10). Other buffers may be selected according to the preference of the user.

The assays yield an FI that is the ratio of the highest restriction enzyme concentration not to show apparent star activity as determined by the presence of bands associated with star activity to the restriction enzyme concentration that completely digests 1 μg of standard DNA substrate in 50 μl reaction for 1 hour at a defined temperature in a standard NEB buffers. In FIGS. 6-17, a box is placed in the figures to show star activity bands. In embodiments of the invention, the FI is for example preferably at least 250 for example greater than 500 for example greater than 1000, for example, greater than 5000.

A fidelity improvement value is calculated as a ratio of the FI of the variant divided by the FI of the non-mutant enzyme. In an embodiment of the invention, the improvement value is for example preferably at least 2, for example, at least 4, for example, at least 8, for example, at least 16.

In one embodiment, the FI refers to the ratio of the highest restriction enzyme amount not to show apparent star activity to the amount that completely digests 1 μg of standard DNA substrate in 50 μl reaction for 1 hour at specific temperature in standard NEB buffers.

TABLE 1 Summary of properties of HF enzymes SEQ ID Enzyme Sub FI1′ FI2′ FI3′ FI4′ Example No. PvuI-HF pXba ≧2000 (⅛) ≧16000 (1) ≧4000 (¼) ≧16000 (1) 1 1 HindIII-HF λ ≧260000 (½) ≧260000 (½) ≧250 ( 1/2000) ≧520000 (1) 2 2 DraIII-HF λ ≧120 ( 1/16) ≧1000 (½) ≧32 ( 1/64) ≧2000 (1) 3 3 KpnI-HF pXba ≧1000000 (1) ≧1000000 (1) ≧30000 ( 1/500) ≧1000000 (1) 4 4 StyI-HF λ ≧4000 (½) 2000 (1) ≧16 ( 1/250) 4000 (½) 5 5 BsaJI-HF pBR322 ≧1000 (¼) ≧4000 (1) ≧4000 (1) ≧4000 (1) 6 6 BsaWI-HF pXba 8 ( 1/64) 120 (1) ≧120 (1)) ≧4000 (1) 7 7 BglI-HF λ ≧4000 (½) ≧8000 (1) ≧500 ( 1/16) ≧8000 (1) 8 8 BsrDI-HF pBR322 ≧120 (⅛) ≧500 (1) ≧64 ( 1/16) ≧1000 (1) 9 9 NsiI-HF pXba ≧250 ( 1/32) ≧1000 (⅛) ≧500 ( 1/16) ≧8000 (1) 10 10 DpnII-HF λ(—) 4000 (¼) 2000 (⅛) 64 ( 1/128) 8000 (1) 11 11 BclI-HF λ(—) ≧250 ( 1/32) ≧500 (¼) ≧32 ( 1/64) ≧2000 (1) 12 12 BglII-HF pXba ≧8000 (⅛) ≧128000 (1) 2000 (½) ≧32000 (¼) 13 13 BstEII-HF λ ≧64 ( 1/32) ≧1000 (½) ≧32 ( 1/64) ≧2000 (1) 14 14 BanII-HF λ(—) ≧4000 (1) ≧2000 (½) ≧500 (⅛) ≧2000 (½) 15 15 PspGI-HF pBC4 ≧1000 (¼) ≧4000 (1) ≧4000 (1) ≧4000 (1) 16 16 SpeI-HF T7 ≧4000 (½) ≧250 (⅛) ≧120 (½) ≧1000 (1) 17 17 BsmAI-HF FX174 ≧4000 (1) ≧2000 (½) ≧500 (⅛) ≧4000 (1) 18 18 BstXI-HF λ ≧500 (½) ≧1000 (1) ≧500 (½) ≧1000 (1) 19 19 SfiI-HF pBC4 250 (½) ≧1000 (⅛) ≧32 ( 1/250) ≧8000 (1) 20 20 PmeI-HF pXba ≧2000 (⅛) ≧500 ( 1/16) ≧32 ( 1/250) ≧8000 (1) 21 21 SmaI-HF pXba ≧2000 ( 1/500) ≧32000 ( 1/32) ≧32 ( 1/32000) ≧256000 (1) 22 22 AatII-HF pXba NC NC NC ≧1000 (1) 23 23 ApoI-HF pXba ≧2000 (½) ≧4000 (1) ≧1000 (¼) ≧2000 (½) 24 24 BsmBI-HF λ 32 (½) 120 (½) ≧120 (½) 250 (1) 25 25 BmtI-HF pXba 25600 (¼) 25600 (¼) 2000 ( 1/500) 1000000 (1) 26 26 BstNI-HF pBR322 ≧120 (½) ≧500 (1) ≧120 (¼) 500 (1) 27 27 MluI-HF λ ≧16000 (½) ≧32000 (1) ≧2000 ( 1/16) ≧32000 (1) 28 28 BanI-HF λ ≧1000 (½) ≧250 (⅛) ≧250 (⅛) ≧2000 (1) 29 29 KasI-HF pBR322 ≧8000 (½) ≧16000 (1) ≧2000 (⅛) ≧16000 (1) 30 30 NruI-HF λ ≧64 ( 1/250) ≧1000 ( 1/16) ≧100 ( 1/16) ≧16000 (1) 31 31 NspI-HF pUC19 ≧4000 (1) 500 (1) ≧250 (⅛) 500 (1) 32 32 BsrFI-HF pBR322 ≧500 (1) ≧64 (⅛) ≧100 ≧500 (1) 33 33

Diluent (Dil) A, B and C and Buffers 1-4 are defined in the NEB catalog 2009/10 page 87.

EXAMPLES Example 1 Engineering of High Fidelity (HF) PvuI 1. Expression of PvuI

PvuI was expressed in E. coli transformed with pUC19-PvuIR and pACYC184-PvuIM, each containing PvuI endonuclease and methylase genes. The cells were grown at 30° C. overnight in LB with Amp and Cam.

2. Mutagenesis of PvuI-HF

All residues Cys, Asp, Glu, Gly, His, Lys, Asn, Pro, Gln, Arg, Ser, Thr were changed to Ala at positions 7, 8, 11, 12, 16, 17, 20, 21, 22, 23, 26, 28, 29, 30, 31, 34, 35, 36, 38, 40, 42, 44, 45, 46, 48, 49, 53, 55, 57, 59, 61, 63, 65, 66, 67, 69, 70, 71, 72, 73, 77, 78, 80, 81, 82, 87, 88, 90, 92, 93, 96, 97, 101, 102, 104, 106, 107, 108, 109, 110, 111, 115, 116, 119, 120, 121, 122, 126, 127, 129, 131, 132, 135, 138, 139, 144, 146, 147, 148, 150, 151, 152, 154, 155, 157, 158, 160, 161, 162, 163, 167, 169, 170, 172, 173, 174, 178, 180, 182, 183, 184, 185, 186, 187, 189, 192, 194, 195, 196, 201, 202, 203, 205, 206, 210, 211, 214, 215, 218, 219, 220, 221, 226, 230, 231, 232, 233, 235, 236, 238, 239, 240, 241, 246, 247, 248, 249, 251, 253, 254; while Tyr was changed to Phe at positions 18, 52, 56, 84, 91, 130, 143, 165, 204, 242.

The mutagenesis methods were inverse PCR with paired primers followed by DpnI-digestion. The treated product was then transformed into E. coli strain ER2683.

3. Selection of PvuI-HF

Selection of PvuI-HF was achieved using comparison of activity in NEB3 and NEB4 (New England Biolabs, Inc., Ipswich, Mass. (NEB) using pXba DNA as substrate. PvuI-WT has more activity in NEB3. The one with more activity in NEB4 was selected. 6 mutants were found to have more activity in NEB4: S36A, K77A, P154A, E163A, Y165F and K185A. P154A had much higher activity than WT in NEB4. Normally, the one with highest activity in NEB4 was the one with improved star activity. PvuI(P154A) was designated as PvuI-HF. This is the first time that an effective mutation was a Proline to Alanine mutation.

4. Purification of PvuI-HF

Two liters of cell ER2683(pUC19-PvuI(P154A), pACYC184-PvuIM)) were grown in LB with 100 μg/ml Amp and 33 μg/ml at 30° C. for overnight. The cells were harvested and sonicated in 20 ml 10 mM Tris-HCl, pH7.5, 50 mM NaCl. After a centrifugation at 15,000 rpm for 30 minutes, the supernatant was loaded on the 5 ml HiTrap™ Heparin HP column (GE Healthcare, now Pfizer, Inc., Piscataway, N.J.) pre-balanced by the same buffer by syringe injection. The column was then loaded on the system by the following procedure: 48 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl, 100 ml 10 mM Tris-HCl, pH 7.5, 50 mM-1M NaCl linear gradient and followed by a 10 ml 10 mM Tris-HCl, pH 7.5, 1M NaCl step. The eluted fractions were then tested for activity. The fractions with highest activity were further concentrated by Vivaspin® 15R (Vivascience, now Sartorius Vivascience GmbH, Goettingen, Germany) and stored in glycerol at −20° C.

5. Comparison of PvuI-HF and PvuI-WT

The FIs of PvuI-HF and PvuI-WT have been determined separately on pXba DNA in four NEB buffers with diluent B. The comparison is shown in FIG. 1, and the result is listed in Table 2 (below).

TABLE 2 Comparison of PvuI-HF and PvuI-WT PvuI-HF PvuI-WT Improvement Buffer Activity FI Activity FI Factor NEB1 12.5%  ≧2000  6.3% 32 ≧64 NEB2 100% ≧16000  25% 32 ≧500 NEB3  25% ≧4000 100% 32 ≧125 NEB4 100% ≧16000 12.5%  32 ≧500

PvuI-HF performed best in NEB2 and NEB4, in which the FI was ≧16,000; WT PvuI performed best in NEB3, in which the FI was 32. So the overall improvement factor was ≧16,000/32=≧500.

Example 2 Engineering of HF HindIII

HindIII recognizes and digests at A/AGCTT as described in Example 21 of International Publication No. WO 2009/009797. A mutant HindIII(K198A) was selected as the HF version of the HindIII. Further characterization of this mutant revealed that though the performance of HindIII(K198A) on one hour scale was excellent, it did not perform well in the overnight digestion. While searching for more mutants, HindIII(Q148A) was also found to be partially good. A further step toward greater improvement was to change the Alanine to all other amino acid residues. Among those, HindIII(Q148I) was found to be excellent in both one hour and overnight reaction, and designated to be HindIII-HF (FIG. 2).

The HindIII-HF was expressed in ER3081 (pUC19-HindIIIR(Q148I)M). The growth and purification methods were performed according to WO/2009/009797.

The following table (Table 3) compares the FIs of HindIII-HF and HindIII-WT.

TABLE 3 Comparison of HindIII-HF and HindIII-WT HindIII-HF HindIII-WT Improvement Buffer Activity FI Activity FI Factor NEB1 50% ≧260000 25% 32 ≧8000 NEB2 50% ≧260000 100%  250 ≧1000 NEB3 0.05%  ≧250 25% 4000 ≧ 1/32 NEB4 100%  ≧520000 50% 32 ≧16000 

The HindIII-HF had the best activity in NEB4; the FI of HindIII-HF in NEB4 was ≧520000; the WT HindIII had the best activity in NEB2. The FI of HindIII-WT in NEB2 was 250. So the overall improvement factor was ≧2,000.

Example 3 Engineering of HF DraIII 1. Expression of DraIII

DraIII recognizes and digests at CACNNN/GTG. DraIII was expressed in E. coli ER3081 with pAGR3-DraIIIR ( ) and pACYC-DraIIIM ( ). The cells were grown at 37° C. overnight in LB with Amp and Cam.

2. Mutagenesis of DraIII

The length of DraIII protein is 227 amino acids. Total 132 amino acid sites of DraIII protein were initially designed to be mutated into Ala is (or Phe). Cys, Asp, Glu, Phe, His, Lys, Met, Asn, Gln, Arg, Ser, Thr, Gly and Trp were mutated to Ala. Try was mutated to Phe. These were: 7, 9, 10, 11, 12, 14, 15, 16, 17, 18, 20, 21, 22, 23, 28, 29, 31, 32, 34, 35, 37, 40, 42, 43, 44, 45, 47, 51, 54, 55, 57, 58, 59, 60, 64, 65, 66, 67, 68, 72, 73, 74, 76, 77, 82, 83, 84, 88, 89, 90, 91, 93, 94, 95, 96, 99, 101, 102, 104, 106, 107, 108, 111, 112, 113, 114, 115, 117, 120, 121, 123, 124, 127, 128, 130, 136, 137, 138, 139, 140, 141, 142, 144, 145, 146, 147, 150, 154, 155, 156, 157, 158, 160, 161, 165, 167, 169, 170, 171, 172, 173, 175, 176, 180, 181, 183, 184, 185, 187, 189, 190, 192, 193, 196, 198, 199, 200, 201, 202, 205, 207, 208, 209, 211, 212, 213, 214, 216, 217, 218, 219, 22, and 223.

The point mutagenesis of the selected mutations was done by inverse PCR. The PCR reaction in a reaction volume of 100 μl, contained 2 μl of each PCR primer, 1 μl pAGR3-DraIIIR, 400 μM dNTP, 4 units of Deep Vent™ DNA polymerase (NEB), and 10 ul 10× Thermopol buffer with additional water.

The PCR reaction conditions were 94° C. for 5 min, followed by 25 cycles of 94° C. 30 sec, 55° C. 60 sec, 72° C. 4 min and a final extension time is at 72° C. for 7 mins. The PCR product was digested by 20 units of DpnI for 1 hour. The digested product was transformed into E. coli ER3081(pACYC-DraIIIM).

3. Selection of DraIII-HF

Four colonies of each mutation were grown up in LB with Amp and Cam at 37° C. overnight. The standard cognate and star activity assays of DraIII were performed using pXba as substrate in NEB4 buffer and 10% glycerol.

The mutants S15A, H20A, E34A, M58A, Q95A, R106A, K108A, T181A, R187A, R199A, N202D, T181G, T181N, T181Q, T181C, T181V, T181L, T181I, T181M, D55A, D55S, D55C, D55G, D55N, T12A, H20A, E34A, H45A, T57A, M58A, T60A, S66A, R76A, F90A, M94A, T101A, C115A, F169A, N172A, R173A, H189A, N193A and Q95A/K104A were picked out in screening assays. After several rounds of comparison in different conditions and substrates, DraIII(T181A) was found to be a preferred mutant, retaining high cleavage high activity, but displaying substantially reduced star activity. DraIII (T181A) was labeled DraIII-HF.

4. Comparison of DraIII-HF and DraIII-WT

The DraIII-WT and DraIII-HF (T181A) proteins were purified using Heparin and Source 15S Column. The assay condition for detailed comparison was as follows: NEB4 (or NEB1, 2, 3), 37° C., 1 h; 2 μl purified protein in 20 μl reaction system; lambda DNA as substrate. The comparison is shown in FIGS. 3A and 3B, and the result is listed in Table 4.

TABLE 4 Comparison of DraIII-HF and DraIII-WT DraIII-HF (T181A) DraIII-WT Improvement Substrate Activity FI Activity FI factor Buffer1 6.25% ≧120 16% 16 ≧8 Buffer2  50% ≧1000 100%  2 ≧500 Buffer3 1.56% ≧32 50% 2 ≧16 Buffer4  100% ≧64000 50% 0.5 ≧128000

DraIII-HF has most activity in NEB4, in which the FI was at least 64,000; the DraIII-WT has most activity in NEB2, in which the FI is 2. The is overall FI improvement factor was at least 32,000 fold.

Example 4 Engineering of HF KpnI

KpnI recognizes and digests at GGTAC/C as described in Example 26 of International Publication No. WO 2009/009797. A triple mutant KpnI(D16N/E132A/D148E) was selected as the high fidelity version of the KpnI. While D148E and E132A were introduced by site-directed mutagenesis, the D16N was introduced by PCR. Further characterization of the mutations in this triple mutant revealed that the removal of the E132A will further improve the restriction enzyme, especially in the aspect of the enzyme specific activity. The triple mutant KpnI(D16N/E132A/D148E) has a specific activity of 200,000 units/mg protein, while KpnI(D16N/D148E) has a specific activity of 1,800,000 units/mg protein. The double mutant is 9 times more active than the previous triple mutant, so the double mutant KpnI(D16N/D148E) was designated as the KpnI-HF.

The KpnI-HF was expressed in ER2523(pAGR3-KpnI(D16N/D148E), pSYX20-KpnIM). The growth and purification methods were performed according to WO/2009/009797.

The following table (Table 5) compares the FIs of KpnI-HF and KpnI WT.

TABLE 5 Comparison of KpnI-HF and KpnI-WT KpnI-HF KpnI-WT Relative Relative Improvement Buffer Activity FI Activity FI factor NEB1  100% ≧1,000,000 100% 16  62,500 NEB2  100% ≧1,000,000  25% 16  62,500 NEB3  0.2%   ≧30,000  6%  8  3,750 NEB4  100% ≧1,000,000  50%  4 250,000

The KpnI WT had the best activity in NEB1, the FI of KpnI-WT in NEB1 was 16; the KpnI-HF had the best activity in NEB1, NEB2 and NEB4. The FI of KpnI-HF in these three buffers were all highest at 1,000,000. The overall improvement factor was 62,500.

Example 5 Engineering of HF StyI 1. Expression of StyI

StyI recognizes and digests at C/CWWGG. StyI was expressed in E. coli (ER2833) with pACYC-StyIM and placzz1-StyIR. The cells were grown at 37° C. overnight in LB with Amp and Cam.

2. Mutagenesis of StyI

The point mutagenesis of the selected mutations was done by inverse PCR. 237 amino acid mutations were made in StyI as follows: Cys, Asp, Glu, Phe, His, Lys, Met, Asn, Gln, Arg, Ser, Thr, Trp were mutated to Ala. Tyr was mutated to Phe. These were at the positions: 7, 9, 10, 11, 12, 14, 16, 22, 23, 24, 25, 26, 28, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 42, 43, 49, 51, 52, 53, 54, 57, 58, 59, 61, 62, 64, 65, 66, 69, 70, 73, 75, 76, 78, 79, 80, 81, 82, 85, 91, 92, 93, 95, 96, 97, 98, 99, 100, 102, 103, 104, 105, 106, 109, 111, 112, 114, 116, 118, 119, 122, 123, 124, 125, 126, 128, 129, 130, 131, 135, 136, 137, 139, 140, 141, 142, 143, 144, 145, 146, 147, 150, 151, 152, 153, 155, 157, 158, 159, 163, 164, 165, 166, 167, 170, 172, 173, 175, 176, 177, 178, 181, 183, 187, 188, 192, 193, 194, 195, 196, 200, 203, 204, 205, 207, 209, 211, 212, 213, 214, 216, 218, 219, 220, 221, 222, 227, 229, 230, 232, 234, 235, 236, 237, 238, 239, 241, 242, 245, 247, 248, 249, 250, 252, 253, 254, 256, 257, 258, 259, 260, 261, 263, 266, 267, 269, 272, 274, 277, 280, 282, 283, 284, 286, 288, 289, 291, 292, 293, 294, 295, 296, 297, 298, 303, 304, 305, 307, 308, 309, 313, 317, 318, 319, 320, 323, 324, 326, 327, 329, 331, 335, 336, 337, 339, 340, 343, 345, 346, 347, 349, 350, 351, 353, 355, 356, 359, 360, 361, 363, 365, 366, 368, 369, 370, 372, 373, 376, 377, 379, 381, and 382.

The method of primer design and PCR can be performed as described in published PCT application WO 2009/0029376 (Example 1). The PCR product was digested with Dpnl and transformed into competent ER2833 (pACYC-StyIM).

3. Selection of StyI-HF

Four colonies of each mutation were grown up in LB with Amp and Cam at 37° C. overnight. The cognate activity assay and star activity assays of StyI were performed using lambda in NEB4 and ExoI buffer and 20% glycerol respectively.

The mutants K75A, N146A and D256A were picked out in screening assays. After several rounds of comparison in different conditions and substrates, K75A was found to be the preferred mutant, retaining high cleavage high activity, but displaying substantially reduced star activity. StyI(K75A) was labeled StyI-HF.

4. Comparison of StyI-HF and StyI-WT

The comparison of StyI-HF and StyI-WT in NEB4 is shown in FIGS. 5A and 5B, and the result is listed in Table 6.

TABLE 6 Comparison of StyI-HF and StyI-WT StyI-HF StyI-WT Relative Relative Improvement Buffer Activity FI Activity FI factor NEB1   50% ≧4000  25% 32 ≧125  NEB2  100%  2000 100% 16 125 NEB3  0.4% ≧16   50% 32 ≧0.5  NEB4   50%  4000  25% 16 250

StyI-WT and StyI-HF had the most activity in NEB2. The FI for StyI-WT was 16 and for StyI-HF was 2000. The overall FI improvement factor was 125.

Example 6 Engineering HF BsaJI 1. Expression of BsaJI

BsaJI was expressed in E. coli transformed with pRRS-BsaJIR+M, which contains BsaJI endonuclease and methylase gene in same plasmid. The cells were grown at 37° C. overnight in LB with Amp and Cam.

2. Mutagenesis of BsaJI-HF

All residues Cys, Asp, Glu, Gly, His, Lys, Asn, Pro, Gln, Arg, Ser, Thr, Phe, Trp, were changed to Ala at positions 9, 10, 14, 17, 18, 19, 20, 22, 23, 24, 27, 30, 32, 35, 39, 42, 43, 48, 50, 51, 52, 53, 55, 56, 57, 60, 61, 65, 66, 67, 68, 70, 71, 72, 73, 78, 79, 81, 83, 84, 86, 87, 88, 90, 91, 92, 94, 95, 99, 101, 103, 104, 106, 110, 111, 113, 114, 117, 119, 120, 121, 123, 127, 129, 131, 132, 134, 136, 138, 140, 141, 142, 147, 152, 153, 157, 158, 159, 162, 163, 165, 166, 167, 169, 170, 175, 178, 181, 183, 184, 185, 186, 187, 188, 189, 194, 196, 197, 198, 199, 200, 202, 203, 204, 206, 211, 212, 213, 214, 215, 216, 218, 220, 222, 225, 226, 227, 228, 229, 230, 231, 233, 238, 239, 240, 241, 246, 247, 249, 250, 251, 252, 253, 254, 255, 257, 260, 262, 265, 267, 268, 269, 270, 271, 273, 274, 276, 277, 280, 281, 282, 283, 285, 287, 288, 290, 291, 293, 294, 295, 298 and 299; while Tyr is changed to Phe at the positions of 21, 59, 62, 77, 89, 105, 130, 191, 208, 272, 286 and 296.

The mutagenesis methods were inverse PCR with paired primers followed by DpnI digestion. The treated product was then transformed into E. coli strain ER3081.

3. Selection of BsaJI-HF

Selection of BsaJI-HF was achieved using comparison of activity in NEB3 and NEB4 using pBR322 DNA as substrate. E198A and D200A have highest activity. D200A has much lower star activity than WT in NEB4. BsaJI (D200A) is designated as BsaJI-HF.

4. Purification of BsaJI-HF

Two liters of cell ER3081 (pRRS-BsaJIR(D200A)+M) were grown in LB with 100 μg/ml Amp, 33 μg/ml Cam and 0.5 mM IPTG at 37° C. for overnight. The cells were harvested and sonicated in 50 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl. After a centrifugation at 15,000 rpm for 30 minutes, the supernatant was loaded on the 5 ml HiTrap™ Heparin HP column (GE Healthcare, now Pfizer, Inc., Piscataway, N.J.) pre-balanced by the same buffer by syringe injection. The column was then loaded on the system by the following procedure: 48 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl, 100 ml 10 mM Tris-HCl, pH 7.5, 50 mM-1M NaCl linear gradient and followed by a 10 ml 10 mM Tris-HCl, pH 7.5, 1M NaCl step. The eluted fractions are then test for activity. The fractions with highest activity were further concentrated by Amicon® Ultra 30 KDa (Millipore, U.S.A; now Merck, Germany). The concentrated BsaJI-HF was then added same volume of glycerol and stored at −20° C.

5. Comparison of BsaJI-HF and BsaJI-WT

The FIs of BsaJI-HF and WT BsaJI have been determined separately on pBR322 DNA in four NEB buffers with diluent A. The result is listed in Table 7.

TABLE 7 Comparison of BsaJI-HF and BsaJI-WT BsaJI-HF BsaJI-WT Improvement Buffer Activity FI Activity FI Factor NEB1  25% ≧1000 100% 64  ≧15 NEB2 100% ≧4000 100% 64  ≧60 NEB3 100% ≧4000  25% 16 ≧250 NEB4 100% ≧4000 100% 64  ≧60

BsaJI-HF performed best in NEB2, 3 and 4, in which the FI was ≧4000; WT BsaJI performed best in NEB1, 2 and 4, in which the FI was 64. So the improvement factor in NEB4 was ≧4000/64≧64.

Example 7 Engineering of HF BsaWI 1. Expression of BsaWI

BsaWI was expressed in E. coli transformed with pLacZZ1-BsaWIR and pACYC-MspIM, each contains BsaWI endonuclease and methylase gene. The cells were grown at 30° C. overnight in LB with Amp and Cam and induced at 30° C. with 0.5 mM of IPTG for 18 hours.

2. Mutagenesis of BsaWI-HF

All residues Cys, Asp, Glu, Gly, His, Lys, Asn, Pro, Gln, Arg, Ser, Thr were changed to Ala at positions 9, 10, 13, 16, 17, 18, 20, 23, 24, 25, 26, 28, 29, 30, 31, 34, 35, 36, 39, 42, 43, 45, 46, 48, 51, 54, 58, 60, 62, 63, 64, 65, 66, 69, 70, 71, 74, 75, 78, 80, 81, 82, 84, 85, 86, 88, 89, 92, 93, 96, 99, 100, 101, 102, 104, 105, 107, 109, 113, 114, 115, 117, 121, 112, 123, 124, 127, 128, 129, 130, 131, 133, 136, 137, 138, 140, 141, 142, 145, 149, 151, 152, 153, 154, 155, 156, 160, 163, 164, 165, 166, 167, 169, 170, 171, 173, 174, 175, 176, 177, 178, 179, 181, 184, 189, 195, 196, 197, 200, 202, 203, 209, 210, 211, 212, 213, 214, 216, 218, 219, 221, 222, 228, 229, 230, 231, 233, 234, 237, 239, 241, 243, 247, 248, 250, 251, 254, 255, 258, 259, 260, 261, 264, and 266; while Tyr is changed to Phe at the positions of 11, 57, 106, 147, 157, 215, 224, 236, and 265.

The mutagenesis methods were inverse PCR with paired primers followed by DpnI digestion. The treated product was then transformed into E. coli strain ER3081.

3. Selection of BsaWI-HF

Selection of BsaWI-HF was achieved using comparison of activity in NEB3 and NEB4 using lambda DNA as substrate. The following mutants showed changes: K229A, E025A, R034A and Q261A. WT BsaWI can complete digestion in both buffers when grown in small culture; Q261A was noticed to only give a stable partial pattern. This could be due to the fact that the mutant grew poorly in small culture. When grown in large culture and purified, the partial pattern was eliminated and the substrate was instead digested completely, and the results also proved to be a is high-fidelity mutant when tested upon the substrate pXba.

4. Purification of BsaWI-HF

Two liters of cell ER3081(pLacZZ1-BwaWI(Q261A), pACYC-MspIM)) were grown in LB with 100 μg/ml Amp and 33 μg/ml at 30° C. for overnight. After 8 hours, the culture was induced with 0.5 mM IPTG. The cells were harvested and sonicated in 20 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl. After a centrifugation at 15,000 rpm for 30 minutes, the supernatant was loaded on the 5 ml HiTrap™ Heparin HP column (GE Healthcare, now Pfizer, Inc., Piscataway, N.J.) pre-balanced by the same buffer by syringe injection. The column was then loaded on the system by the following procedure: 48 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl, 100 ml 10 mM Tris-HCl, pH 7.5, 50 mM-1M NaCl linear gradient and followed by a 10 ml 10 mM Tris-HCl, pH 7.5, 1M NaCl step. The eluted fractions were then tested for activity. The fractions with highest activity were further concentrated by Vivaspin® 15R (Vivascience, now Sartorius Vivascience GmbH, Goettingen, Germany). The concentrated BsaWI-HF was then added an equal volume of glycerol and stored at −20° C.

5. Comparison of BsaWI-HF and BsaWI-WT

The FIs of BsaWI-HF and BsaWI-WT have been determined separately on pXba DNA in four NEB buffers with diluent A. The result is listed in Table 8 (below).

TABLE 8 Comparison of BsaWI-HF and BsaWI-WT BsaWI-HF BsaWI-WT Improvement Buffer Activity FI Activity FI Factor NEB1  1.6%  8 12.5%  4 2 NEB2  100% 120   50%  8 ≧15  NEB3  3.1% ≧250   3.1% 64 ≧4  NEB4  100% ≧4000  100% 16 ≧250

BsaWI-HF is most active in NEB2 and NEB4, in which the best FI is ≧4000; BsaWI-WT is most active in NEB4, in which the FI is 16. The overall improvement factor is ≧4000/16=˜250.

Example 8 Engineering of High Fidelity BglI 1. Expression of BglI

BglI was expressed in E. coli transformed with pUC19-BglIR and pSYX20-BglIM, each contains BglI endonuclease and methylase gene. The cells were grown at 37° C. overnight in LB with Amp and Kan.

2. Mutagenesis of BglI-HF

All residues Cys, Asp, Glu, Gly, His, Lys, Asn, Pro, Gln, Arg, Ser, Thr were changed to Ala at positions 7, 8, 12, 14, 15, 16, 17, 18, 19, 22, 23, 24, 25, 27, 28, 29, 31, 34, 36, 39, 40, 43, 44, 45, 46 47, 48, 50, 52, 54, 5, 57, 60, 61, 65, 67, 68, 70, 71, 72, 73, 75, 76, 77, 78, 79, 81, 84, 86, 87, 88, 91, 92, 94, 95, 96, 99, 100, 101, 102, 103, 105, 107, 108, 110, 112, 113, 114, 115, 116, 117, 118, 122, 123, 124, 125, 128, 130, 131, 132, 134, 135, 136, 152, 158, 159, 160, 161, 163, 164, 165, 166, 167, 170, 172, 173, 174, 176, 177, 178, 179, 180 181, 183, 184, 185, 186, 187, 188, 189, 193, 194, 196, 197, 202, 203, 204, 205, 208, 211, 215, 216, 221, 222, 224, 225, 226, 227, 228, 229, 230, 231, 234, 236, 239, 241, 242, 243, 245, 249, 250, 251, 255, 256, 259, 263, 264, 265, 266, 267, 268, 269, 270, 271, 272, 275, 276, 277, 279, 281283, 286, 287, 289, 290, and 291; while Tyr is changed to Phe at the positions of 19, 13, 33, 53, 66, 119, 127, 153, 199, 218, 233, 252, and 258.

The mutagenesis methods were inverse PCR with paired primers followed by DpnI digestion. The treated product was then transformed is into E. coli strain ER2566.

3. Selection of BglI-HF

Selection of BglI-HF was achieved using comparison of activity in NEB4 using lambda DNA as substrate. BglI-WT has low activity in NEB4, so any mutants with similar or more activity than WT in NEB4 were selected, then they were checked against glycerol for comparison of star activity levels. Only one mutant, K225A, showed similar activity to WT in NEB4 while also decreasing star activity when tested in glycerol. BglI(K225A) is designated as BglI-HF.

4. Purification of BglI-HF

Two liters of cell ER2566(pUC19-BglI(K225A), pSYX20-BglIM) were grown in LB with 100 μg/ml Amp and 33 μg/ml Kan at 37° C. for overnight. The cells were harvested and sonicated in 20 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl. After a centrifugation at 15,000 rpm for 30 minutes, the supernatant was loaded on the 5 ml HiTrap™ Heparin HP column (GE Healthcare, now Pfizer, Inc., Piscataway, N.J.) pre-balanced by the same buffer by syringe injection. The column was then loaded on the system by the following procedure: 48 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl, 100 ml 10 mM Tris-HCl, pH 7.5, 50 mM-1M NaCl linear gradient and followed by a 10 ml 10 mM Tris-HCl, pH 7.5, 1M NaCl step. The eluted fractions were then tested for activity. The fractions with highest activity were further concentrated by Vivaspin® 15R (Vivascience, now Sartorius Vivascience GmbH, Goettingen, Germany). The concentrated BglI-HF was then added to an equal volume of glycerol and stored at −20° C.

5. Comparison of BglI-HF and BglI-WT

The FIs of BglI-HF and WT BglI have been determined separately on lambda DNA in four NEB buffers with diluent B. The comparison is shown in FIG. 6, and the result is listed in Table 9 (below).

TABLE 9 Comparison of BglI-HF and BglI-WT BglI-HF BglI-WT Improvement Buffer Activity FI Activity FI Factor NEB1   50% ≧4000 25.0%  64 ≧62  NEB2  100% ≧8000  100%  64 ≧125 NEB3  6.3% ≧500   100% 250 ≧2  NEB4  100% ≧8000   50%  32 ≧250

BglI-HF was most active in NEB2 and NEB4, in which the FI was ≧8000; BglI-WT is most active in NEB3, in which the FI was 250. The overall improvement factor was ≧8000/250=≧32.

Example 9 Engineering of HF BsrDI 1. Expression of BsrDI

BsrDI enzyme contains two subunits: BsrDIA and BsrDIB.

To obtain a pure BsrDIA subunit, the IMPACT (Intein-Mediated Purification with an Affinity Chitin-Binding Tag) system (NEB cat: E6901) was used for the one-step purification of BsrDIA. Briefly, the BsrDIA gene was sub-cloned into the pTXB1 vector, which was then transformed into a competent strain containing the T7 RNA polymerase, controlled by the lac operon (NEB #ER2566). After screening and sequencing, the corrected strain was selected. Cells were grown in LB media with Ampicillin (100 μg/ml) at 37° C. until the OD₆₀₀ reached 0.5. Then, IPTG was added to reach a final concentration of 0.4 mM for the induction of BsrDIA for 3 hours. Cell culture was then pelleted, resuspended in ice-cold Column Buffer (20 mM Tris-HCl, pH 8.5, 500 mM NaCl) and lysed via sonication. The resulting cell lysate was then centrifuged to remove cellular debris. Next, the supernatant was loaded onto an equilibrated Chitin Column. After washing with the loading buffer, the column was incubated with cleavage buffer (20 mM Tris-HCl, pH 8.5, 500 mM NaCl and 50 mM DTT) at 4° C. overnight. Finally, the BtsI.A protein was eluted with dialysis against the storage buffer (10 mM Tris-HCl pH 7.4, 0.1 mM EDTA, 1 mM DTT, 50 mM KCl and 50% glycerol).

BsrDIB subunit was expressed in E. coli transformed with pUC19-BsrDIBR and pLG-BsrDIM1M2, each contains BsrDI endonuclease and methylase gene. The cells were grown at 37° C. overnight in LB with Amp and Kam.

2. Mutagenesis of BsrDI-HF

All residues of BsrDIB including Cys, Asp, Glu, Gly, His, Lys, Asn, Pro, Gln, Arg, Ser, Thr were changed to Ala at positions 7, 11, 12, 14, 15, 17, 21, 22, 25, 28, 29, 30, 33, 34, 35, 37, 40, 45, 46, 47, 51, 52, 56, 58, 62, 64, 65, 67, 68, 71, 72, 74, 75, 81, 83, 90, 91, 92, 93, 99, 100, 101, 106, 108, 109, 112, 113, 115, 116, 120, 122, 123, 124, 132, 133, 136, 137, 138, 139, 142, 143, 144, 145, 146, 150, 155, 157, 158, 161, 162, 164, 168, 170, 171, 173, 174, 176, 177, 179, 180, 182, 185, 189, 190, 193, 197, 200, 202, 203, 206, 210, 213, 215, 217, 218, 221, 224, 225, 226, 228, 229, 230, 232, 237, 238, 241, 242, 243, 244, 245, 246, 249, 253, 258, 259, 261, 264, 265, 268, 271, 272, 273, 274, 276, 278, 279, 281, 285, 287, 288, 292, 294, 295, 299, 300, 301, 306, 307, 308, 312, 314, 315, 317, 318, 320, 321, 324, 325, 326, 327, 328, 331, 332, 335, 337, 341, 343, 345, 347, 352, 353, 354, 355, 356, 360, 361, 362, 363, 364, 370, 373, 374, 376, 380, 381, 385, 387, 389, 392, 393, 395, 396, 397, 405, 406, 408, 411, 415, 418, 420, 422, 425, 426, 430, 431, 432, 434, 437, 445, 446, 449, 450, 454, 455, 456, 457, 458, 459, 460, 463, 465, 466, 467, 469, 470, 475, 481; while Tyr is changed to Phe at the positions of 9, 38, 63, 87, 118, 129, 169, 178, 198, 216, 251, 286, 291, 303, 357, 358, 367, 371, 402, 442, 443, 448.

The mutagenesis methods were inverse PCR with paired primers followed by DpnI digestion. The treated product was then transformed into E. coli strain ER2566.

3. Selection of BsrDI-HF

Selection of BsrDI-HF was achieved using comparison of star activity between the WT BsrDIB mixed with BsrDIA and the mutant BsrDIB mixed with BsrDIA in NEB4 on pBR322 DNA as substrate. Eight mutants are found to have less star activity in NEB4:H137A, D177A, K363A, K408A, R411A, Q215A, Q226A, Q230A.

To further reduce the star activity, we combine the above mutations to make double mutations: K363A/Q230A, K363A/K408A, Q230A/K408A. Then BsrDI with mutations on BsrDIB of Q230A/K363A is designated as BsrDI-HF.

4. Purification of BsrDI-HF

Two liters of cell ER2566(pUC19-BsrDI(Q230A/K363A), pLG-BsrDIM1M2)) were grown in LB with 100 μg/ml Amp and 33 μg/ml Kam at 37° C. for overnight. The cells were harvested and sonicated in 20 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl. After a centrifugation at 15,000 rpm for 30 minutes, the supernatant was loaded on the 5 ml HiTrap™ Heparin HP column (GE Healthcare, now Pfizer, Inc., Piscataway, N.J.) pre-balanced by the same buffer by syringe injection. The column was then loaded on the system by the following procedure: 48 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl, 100 ml 10 mM Tris-HCl, pH 7.5, 50 mM-1M NaCl linear gradient and followed by a 10 ml 10 mM Tris-HCl, pH 7.5, 1M NaCl step. The eluted fractions are then test for activity. The fractions with highest activity were further concentrated by Vivaspin® 15R (Vivascience, now Sartorius Vivascience GmbH, Goettingen, Germany). The concentrated BsrDI-HF was then added same volume of glycerol and stored at −20° C. condition.

5. Comparison of BsrDI-HF and BsrDI-WT

The FIs of BsrDI-HF and BsrDI-WT have been determined separately on pBR322 DNA in four NEB buffers with diluent A. The result is shown in FIG. 7 and listed in Table 10 (below).

TABLE 10 Comparison of BsrDI-HF and BsrDI-WT BsrDI-HF BsrDI-WT Improvement Buffer Activity FI Activity FI Factor NEB1 12.5% ≧120    6% 1 ≧120  NEB2  100% ≧500   100% 4 ≧120  NEB3   6% ≧64  12.5% 4 ≧16  NEB4  100% ≧1000   25% ½ ≧2000

BsrDI-HF performed best in NEB4, in which the FI was ≧1000; BsrDI-WT performed best in NEB2 and NEB3, in which the FI was 64. So the overall improvement factor was ≧1000/0.5=≧2000.

Example 10 Engineering of HF NsiI 1. Expression of NsiI

NsiI was expressed in E. coli transformed with placzz1-NsiIR and pACYC-NsiIM, each contains NsiI endonuclease and methylase gene. The cells were grown at 37° C. overnight in LB with Amp and Cam.

2. Mutagenesis of NsiI-HF

All residues Cys, Asp, Glu, Gly, His, Lys, Asn, Pro, Gln, Arg, Ser, Thr, Phe, Trp, were changed to Ala at positions 8, 9, 10, 11, 12, 13, 18, 21, 22, 23, 24, 26, 27, 32, 34, 35, 42, 44, 45, 46, 47, 49, 50, 52, 53, 54, 55, 57, 58, 60, 61, 69, 70, 73, 74, 79, 80, 84, 85, 87, 90, 91, 92, 93, 95, 96, 97, 98, 99, 100, 102, 103, 105, 106, 108, 109, 110, 113, 114, 115, 117, 118, 119, 120, 121, 122, 123, 124, 126, 134, 135, 137, 138, 139, 140, 142, 144, 145, 146, 149, 151, 153, 154, 155, 156, 159, 160, 161, 162, 163, 166, 167, 170, 173, 174, 175, 178, 179, 180, 181, 182, 183, 184, 186, 188, 189, 190, 191, 192, 195, 197, 198, 199, 200, 201, 202, 203, 206, 207, 209, 210, 211, 213, 215, 216, 217, 219, 221, 222, 225, 230, 231, 232, 234, 235, 236, 237, 239, 242, 243, 244, 245, 246, 249, 250, 251, 256, 257, 259, 260, 261, 263, 264, 268, 269, 271, 272, 273, 276, 277, 278, 279, 281, 282, 283, 285, 287, 288, 290, 292, 294, 295, 297, 298, 299, 302, 303, 306, 307, 308, 309, 310, 312, 315, 316, 319, 320, 323, 325, 327, 329, 333, 334, 336, 337, 338, 340, 341, 344, 347, 349, 350, 352, 353, 354, 355, 358, 359, 360, 362, 363, 365, 366, 367, 371, 372, 373, 375, 376 and 377; while Tyr is changed to Phe at the positions of 30, 40, 62, 65, 71, 76, 83, 86, 141, 226, 233, 255, 289, 311, 326, 335, 351, 357, 378.

The mutagenesis methods were inverse PCR with paired primers followed by DpnI digestion. The treated product was then transformed into E. coli strain ER3081.

3. Selection of NsiI-HF

Selection of NsiI-HF was achieved using comparison of activity in NEB3 and NEB4 using pXba DNA as substrate. NsiI-WT has more activity in NEB3, the one with more activity in NEB4 were selected. 148 mutants are found to have more activity in NEB4. F376A has much higher activity than WT in NEB4. Normally the one with highest activity in NEB4 is the one with improved star activity. NsiI (F376A) is designated as NsiI-HF.

4. Purification of NsiI-HF

Two liters of cell ER3081 (placzz1-NsiI(F376A), pACYC-NsiIM)) were grown in LB with 100 μg/ml Amp, 33 μg/ml Cam and 0.5 mM IPTG at 37° C. for overnight. The cells were harvested and sonicated in 50 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl. After a centrifugation at 15,000 rpm for 30 minutes, the supernatant was loaded on the 5 ml HiTrap™ Heparin HP column (GE Healthcare, now Pfizer, Inc., Piscataway, N.J.) pre-balanced by the same buffer by syringe injection. The column was then loaded on the system by the following procedure: 48 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl, 100 ml 10 mM Tris-HCl, pH 7.5, 50 mM-1M NaCl linear gradient and followed by a 10 ml 10 mM Tris-HCl, pH 7.5, 1M NaCl step. The eluted fractions are then test for activity. The fractions with highest activity were further concentrated by Amicon Ultra 30 KDa (Millipore, U.S.A; now Merck, Germany). The concentrated NsiI-HF was then added same volume of glycerol and stored in the −20° C. condition.

5. Comparison of NsiI-HF and NsiI-WT

The FIs of NsiI-HF and WT NsiI have been determined separately on pXba DNA in four NEB buffers with diluent A. The result is listed in Table 11 (below).

TABLE 11 Comparison of NsiI-HF and NsiI-WT NsiI-HF NsiI-WT Improvement Buffer Activity FI Activity FI Factor NEB1   3% ≧250   6.3% 32 ≧8  NEB2 12.5% ≧1000   25% 32 ≧30  NEB3   6% ≧500   100% 32 ≧15  NEB4  100% ≧8000 12.5% 32 ≧250

NsiI-HF performed best in NEB4, in which the FI was ≧8000; WT NsiI performed best in NEB3, in which the FI was 32. So the improvement factor in NEB4 was ≧8000/32=≧250.

Example 11 Engineering of HF DpnII 1. Expression of DpnII

DpnII was expressed in E. coli 3081 transformed with pBAD241-DpnII RM. The cells were grown at 30° C. overnight in LB with Amp.

2. Mutagenesis of DpnII

The point mutagenesis of the selected mutations was done by inverse PCR. 189 amino acid mutations were made in DpnII as follows. Cys, Asp, Glu, Phe, His, Lys, Met, Asn, Gln, Arg, Ser, Thr, Trp were mutated to Ala. Try was mutated to Phe. These were: 7, 8, 9, 10, 12, 13, 14, 15, 16, 17, 19, 20, 21, 22, 23, 24, 25, 26, 27, 29, 31, 32, 33, 35, 36, 38, 40, 42, 44, 45, 46, 50, 51, 52, 54, 55, 56, 57, 59, 61, 62, 63, 64, 66, 69, 76, 77, 78, 80, 81, 82, 86, 87, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 104, 105, 106, 107, 108, 109, 111, 112, 113, 116, 117, 118, 120, 121, 122, 125, 126, 129, 130, 132, 135, 138, 139, 140, 141, 143, 144, 145, 146, 147, 149, 150, 151, 152, 153, 156, 157, 158, 160, 161, 162, 164, 168, 169, 171, 172, 173, 175, 176, 177, 178, 180, 181, 183, 184, 186, 188, 189, 191, 192, 193, 195, 196, 198, 199, 200, 201, 202, 205, 206, 207, 208, 211, 214, 216, 217, 218, 219, 221, 223, 224, 226, 227, 228, 229, 230, 231, 232, 233, 234, 236, 237, 238, 239, 240, 241, 244, 246, 247, 248, 249, 251, 252, 254, 256, 257, 258, 259, 260, 261, 262, 264, 265, 266, 267, 268, 272, 274, 275, 277, 278, 280, 281 and 282.

The method of primer design and PCR is similar to that described previously. The PCR product was digested with Dpnl and transformed into competent E. coli 3081.

3. Selection of DpnII-HF

Four colonies of each mutation were grown up in LB with Amp at 37° C. overnight. The standard screening assays of DpnII were performed using dam⁻ lamda substrate in NEB4 buffer and 5% glycerol.

The mutants R78A, T140A, E152A, R199A, and F217A were picked out from screening assay. After several rounds of comparison in different conditions and substrates, R199A was chose as candidate, retaining high canonical enzyme activity, but displaying substantially reduced star activity. R199A was labeled as DpnII-HF.

4. Purification of DpnII-HF

Two liters of cell E. coli 3081 (pBAD241.DpnII.RM (R199A)) were grown in LB with 100 ug/ml Amp at 30° C. for overnight. The cells were harvested and sonicated in 20 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl. After a centrifugation at 15,000 rpm for 30 minutes, the supernatant was loaded on the 5 ml HiTrap™ Heparin HP column (GE Healthcare, now Pfizer, Inc., Piscataway, N.J.) pre-balanced by the same buffer by syringe injection. The column was then loaded on the system by the following procedure: 48 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl, 100 ml 10 mM Tris-HCl, pH 7.5, 50 mM-1M NaCl linear gradient and followed by a 10 ml 10 mM Tris-HCl, pH 7.5, 1M NaCl step. The eluted fractions are then test for activity. The fractions with highest activity were further concentrated. The concentrated Bmt-HF was then added same volume of glycerol and stored in the −20° C. condition.

5. Comparison of DpnII-HF and DpnII-WT

DpnII-HF was 2-fold serial diluted with B and reacted in four NEB buffers, and DpnII-WT was 2-fold serial diluted and reacted in four NEB buffers. The result is listed in Table 12.

TABLE 12 Comparison of DpnII-HF and DpnII-WT DpnII-HF DpnII-WT Improvement Buffer Activity FI Activity FI Factor NEB1   50% 4000  25%  1 4000 NEB2   25% 2000  25%  1 2000 NEB3  0.8%  64 100% 32   2 NEB4  100% 8000  25%  1 8000

DpnII-HF performed best in NEB4, in which the preferred FI was =8000; DpnII performed best in NEB3, where the FI was 32. The overall FI improvement factor was 8000/32=250.

Example 12 Engineering of High Fidelity BclI 1. Expression of BclI

BclI was expressed in E. coli transformed with pRRS-BclIR and pACYC184-BclIM, each contains BclI endonuclease and methylase gene. The cells were grown at 37° C. overnight in LB with Amp.

2. Mutagenesis of BclI-HF

All residues Cys, Asp, Glu, Gly, His, Lys, Asn, Pro, Gln, Arg, Ser, Thr were changed to Ala at positions 9, 10, 11, 12, 19, 22, 23, 24, 26, 28, 29, 30, 31, 35, 37, 38, 40, 42, 44, 46, 47, 49, 51, 53, 54, 55, 58, 59, 62, 65, 67, 69, 72, 73, 74, 75, 76, 80, 82, 83, 85, 86, 89, 93, 94, 95, 96, 97, 98, 99, 101, 103, 105, 107, 108, 109, 110, 111, 112, 113, 114, 115, 120, 124, 128, 129, 130, 132, 136, 137, 138, 139, 143, 144, 145, 149, 150, 151, 152, 154, 156, 160, 162, 163, 164, 166, 167, 170, 171, 172, 174, 175, 178, 179, 180, 182, 183, 188, 190, 191, 195, 196, 197, 199, 200, 201, 204, 205, 208, 209, 210, 212, 213, 215, 217, 218, 220, 221, 222, 223, 224, 225, 226, 228, 229, 234, 235, 237, 238, 241, 243, 244, 245, 249, 252, 255, 257, 260, 261, 265, 266, 267, 270, 271, 273, 274, and 277; while Tyr is changed to Phe at the positions of 17, 27, 36, 63, 66, 77, 87, 100, 116, 118, 133, 142, 147, 157, 192, 193, 194, 207, 212, 231, 236, and 246.

The mutagenesis methods were inverse PCR with paired primers followed by DpnI digestion. The treated product was then transformed into E. coli strain ER2984.

3. Selection of BclI-HF

Selection of BclI-HF was achieved using comparison of activity in glycerol and NEB4 using dam− lambda DNA as the substrate. Once lower star activity was suspected, mutants were also compared with normal activity in water and NEB4 on the same substrate. Mutants with similar activity to WT in NEB4 and also with the potential to have lower star activity were selected. 6 mutants are found to have such characteristics: G26A, P105A, T195A, Q210A, Y147F, and Y193F. Several mutants (K114A, T197A, S245A, D252A, and Y027F) showed lower activity in water, but decreased star activity as well; they usually had higher activity cognate activity than WT under high glycerol conditions. One mutant showed higher activity than WT and also lower star activity: Y192F. BclI(Y192F) is designated as BclI-HF.

4. Purification of BclI-HF

Two liters of cell ER2984(pRRS-BclI(Y192F), pACYC184-BclIM)) were grown in LB with 100 μg/ml Amp at 37° C. for overnight. The cells were harvested and sonicated in 20 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl. After a centrifugation at 15,000 rpm for 30 minutes, the supernatant was loaded on the 5 ml HiTrap™ Heparin HP column (GE Healthcare, now Pfizer, Inc., Piscataway, N.J.) pre-balanced by the same buffer by syringe injection. The column was then loaded on the system by the following procedure: 48 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl, 100 ml 10 mM Tris-HCl, pH 7.5, 50 mM-1M NaCl linear gradient and followed by a 10 ml 10 mM Tris-HCl, pH 7.5, 1M NaCl step. The eluted fractions were then tested for activity. The fractions with highest activity were further concentrated by Vivaspin® 15R (Vivascience, now Sartorius Vivascience GmbH, Goettingen, Germany). The concentrated BclI-HF was then added to an equal volume of glycerol and stored at −20° C.

5. Comparison of BclI-HF and BclI-WT

The FIs of BclI-HF and BclI-WT have been determined separately on dam− lambda DNA in four NEB buffers with diluent A. The comparison is shown in FIG. 8, and the result is listed in Table 13 (below).

TABLE 13 Comparison of BclI-HF and BclI-WT BclI-HF BclI-WT Improvement Buffer Activity FI Activity FI Factor NEB1 12.5% ≧250   50% 120 ≧2  NEB2  100% ≧500  100%  32 ≧16 NEB3   25% ≧32   50%  64 ≧½ NEB4  100% ≧2000 100%  32 ≧60

BclI-HF performed best in NEB2 and NEB4, in which the best FI was ≧2000; BclI-WT performed best in NEB2 and NEB4, in which the FI was 32. The overall improvement factor is ≧2000/32=≧64.

Example 13 Engineering of HF BglII 1. Expression of BglII

BglII was expressed in E. coli transformed with pLacZZ-BglIIR and pACYC-BglIIM, each contains BglII endonuclease and methylase gene. The cells were grown at 37° C. overnight in LB with Amp and Cam.

2. Mutagenesis of BglII-HF

All residues Cys, Asp, Glu, Gly, His, Lys, Asn, Pro, Gln, Arg, Ser, Thr were changed to Ala at positions 2, 4, 6, 7, 9, 10, 12, 13, 16, 18, 20, 21, 22, 24, 25, 26, 29, 30, 33, 35, 37, 38, 39, 41, 42, 45, 48, 49, 53, 54, 55, 58, 59, 60, 64, 65, 66, 67, 68, 69, 74, 75, 76, 77, 78, 81, 82, 84, 85, 87, 88, 89, 90, 93, 95, 96, 97, 98, 101, 104, 105, 106, 108, 109, 110, 112, 113, 114, 115, 116, 117, 118, 120, 121, 122, 124, 125, 131, 132, 134, 135, 136, 139, 140, 141, 142, 146, 147, 149, 150, 151, 153, 154, 157, 159, 161, 162, 166, 172, 173, 174, 175, 176, 177, 179, 182, 183, 184, 187, 188, 189, 191, 192, 193, 195, 196, 197, 198, 199, 201, 203, 206, 207, 208, 209, 211, 212, 213, 214, 215, 216, 217, 219, 222; while Tyr is changed to Phe at the positions of 8, 56, 99, 144, 145, 158, 185, and 190.

The mutagenesis methods were inverse PCR with paired primers followed by DpnI digestion. The treated product was then transformed into E. coli strain ER3081.

3. Selection of BglII-HF

Selection of BglII-HF was achieved using comparison of activity in NEB3 and NEB4 using pXba DNA as substrate. BglII-WT has more activity in NEB3, so the mutants with more activity in NEB4 were selected. All mutants with more activity were then compared to WT activity in glycerol to check for star activity. Normally the mutant with the highest activity in NEB4 is the one with improved star activity. The mutants that were most promising (H10A, N208A, K48A, K74A, R75A, Y56F, K58A, M117A) were finally tested with Exol buffer in water, which can promote star activity in BglI-WT. One mutant, N208A showed decreased star activity in NEB4 and increased overall activity. In small culture, this mutant can appear to is have stable partial activity, which we have determined is another indicator that the fidelity has changed. BglII(N208A) is designated as BglII-HF.

4. Purification of BglII-HF

Two liters of cell ER3081(pLacZZ-BglII(N208A), pACYC-BglIIM)) were grown in LB with 100 μg/ml Amp and 33 μg/ml at 30° C. for overnight. The cells were harvested and sonicated in 20 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl. After a centrifugation at 15,000 rpm for 30 minutes, the supernatant was loaded on the 5 ml HiTrap™ Heparin HP column (GE Healthcare, now Pfizer, Inc., Piscataway, N.J.) pre-balanced by the same buffer by syringe injection. The column was then loaded on the system by the following procedure: 48 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl, 100 ml 10 mM Tris-HCl, pH 7.5, 50 mM-1M NaCl linear gradient and followed by a 10 ml 10 mM Tris-HCl, pH 7.5, 1M NaCl step. The eluted fractions were then tested for activity. The fractions with highest activity were further concentrated by Vivaspin® 15R (Vivascience, now Sartorius Vivascience GmbH, Goettingen, Germany). The concentrated BglII-HF was then added an equal volume of glycerol and stored at −20° C.

5. Comparison of BglII-HF and BglII-WT

The FIs of BglII-HF and BglII-WT have been determined separately on pXba DNA in four NEB buffers with diluent B. The comparison is shown in FIG. 9, and the result is listed in Table 14 (below).

TABLE 14 Comparison of BglII-HF and BglII-WT BglII-HF BglII-WT Improvement Buffer Activity FI Activity FI Factor NEB1 12.5% ≧8000    25% 250 ≧32  NEB2  100% ≧128000  100%  64 ≧2000 NEB3   50% ≧2000   100% 120 ≧16  NEB4   25% ≧32000   6.3%  16 ≧2000

BglII-HF performed best in NEB2, in which the FI was ≧128000; BglII-WT performed best in NEB3, in which the FI was 120. The overall improvement factor was ≧128000/120=≧1000.

Example 14 Engineering of HF BstEII 1. Expression of BstEII

BstEII was expressed in E. coli transformed with pUC19-BstEIIR and pACYC-BstEIIM, each contains BstEII endonuclease and methylase gene. The cells were grown at 37° C. overnight in LB with Amp and Cam.

2. Mutagenesis of BstEII-HF

All residues Cys, Asp, Glu, Gly, His, Lys, Asn, Pro, Gln, Arg, Ser, Thr were changed to Ala at positions 7, 9, 10, 14, 17, 20, 21, 22, 25, 26, 29, 30, 32, 36, 37, 40, 41, 44, 47, 48, 49, 50, 51, 52, 54, 57, 58, 60, 61, 62, 63, 64, 65, 67, 68, 69, 72, 75, 76, 79, 80, 81, 82, 83, 85, 88, 89, 90, 91, 92, 94, 95, 98, 99, 101, 102, 103, 105, 106, 111, 112, 113, 116, 117, 118, 119, 120, 121, 122, 123, 130, 132, 133, 134, 135, 136, 137, 138, 140, 142, 143, 147, 150, 151, 152, 154, 155, 157, 160, 161, 162, 163, 165, 166, 167, 171, 172, 175, 176, 178, 179, 180, 182, 184, 189, 190, 191, 192, 193, 194, 195, 199, 202, 204, 205, 206, 207, 208, 209, 211, 212, 213, 214, 215, 216, 217, 218, 219, 220, 221, 222, 224, 225, 227, 228, 232, 233, 234, 236, 238, 243, 244, 245, 246, 247, 251, 252, 255, 256, 258, 261, 262, 264, 265, 266, 272, 274, 277, 278, 279, 281; while Tyr is changed to Phe at the positions of 8, 15, 24, 27, 35, 43, 77, 129, 131, 139, 156, 188, 203, 229, 257, and 263.

The mutagenesis methods were inverse PCR with paired primers followed by DpnI digestion. The treated product was then transformed is into E. coli strain ER2683.

3. Selection of BstEII-HF

Selection of BstEII-HF was achieved using comparison of activity in NEB3 and NEB4 using lambda DNA as substrate. WT BstEII has more activity in NEB3, so the mutants with more activity in NEB4 were selected. Seven mutants were found to have improved activity in NEB4: K014A, Q069A, E099A, R105A, R117A, G135A, and Y035F. R105A had the most difference in activity compared to WT in NEB4 and water and also showed decreased star activity when with tested in glycerol with Exol buffer, a condition which shows star activity in WT. BstEII(R105A) is designated as BstEII-HF.

4. Purification of BstEII-HF

Two liters of cell ER2683(pUC19-BstEII(R105A), pACYC-BstEIIM)) were grown in LB with 100 μg/ml Amp and 33 μg/ml at 30° C. for overnight. The cells were harvested and sonicated in 20 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl. After a centrifugation at 15,000 rpm for 30 minutes, the supernatant was loaded on the 5 ml HiTrap™ Heparin HP column (GE Healthcare, now Pfizer, Inc., Piscataway, N.J.) pre-balanced by the same buffer by syringe injection. The column was then loaded on the system by the following procedure: 48 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl, 100 ml 10 mM Tris-HCl, pH 7.5, 50 mM-1M NaCl linear gradient and followed by a 10 ml 10 mM Tris-HCl, pH 7.5, 1M NaCl step. The eluted fractions were then tested for activity. The fractions with highest activity were further concentrated by Vivaspin® 15R (Vivascience, now Sartorius Vivascience GmbH, Goettingen, Germany). The concentrated BstEII-HF was then added an equal volume of glycerol and stored at −20° C.

5. Comparison of BstEII-HF and WT BstEII

The FIs of BstEII-HF and WT BstEII have been determined separately on lambda DNA in four NEB buffers with diluent A. The is comparison is shown in FIG. 10, and the result is listed in Table 15 (below).

TABLE 15 Comparison of BstEII-HF and BstEII-WT BstEII-HF BstEII-WT Improvement Buffer Activity FI Activity FI Factor NEB1   3% ≧64   50% 16 ≧4  NEB2   50% ≧1000 100%  4 ≧250 NEB3  1.6% ≧32   50% 16 ≧2  NEB4  100% ≧2000 100%  4 ≧500

BstEII-HF performed best in NEB4, in which the FI was ≧2000; BstEII-WT performed best in NEB2 and NEB4, in which the FI was 4. The overall improvement factor is ≧2000/4=≧500.

Example 15 Engineering of HF BanII 1. Expression of BanII

BanII was expressed in E. coli transformed with pUC19-BanIIR and pACYC1-BanIIM, each contains BanII endonuclease and methylase gene. The cells were grown at 37° C. overnight in LB with Amp and Cam.

2. Mutagenesis of BanII-HF

All residues except Tyr (and those that were already Ala) were changed to Ala at positions 7, 8, 9, 10, 12, 16, 17, 20, 21, 23, 24, 25, 26, 28, 29, 24, 31, 32, 35, 38, 39, 43, 44, 45, 47, 49, 54, 59, 61, 63, 64, 66, 67, 71, 72, 73, 74, 75, 77, 78, 81, 83, 84, 87, 88, 92, 94, 95, 96, 97, 99, 100, 103, 104, 105, 106, 107, 108, 111, 112, 113, 115, 117, 118, 120, 121, 122, 123, 126, 127, 128, 129, 130, 131, 135, 139, 142, 143, 145, 146, 147, 148, 149, 152, 153, 155, 156, 163, 166, 167, 168, 169, 170, 171, 173, 175, 176, 178, 179, 180, 181, 183, 184, 186, 190, 191, 194, 195, 196, 198, 199, 200, 207, 208, 211, 213, 214, 215, 216, 219, 220, 221, 222, 224, 226, 229, 230, 231, 232, 234, 235, 236, 237, 239, 240, 242, 245, 246, 247, 248, 252, 254, 256, 257, 258, 259, 261, 262, 263, 264, 266, 267, 270, 271, 272, 274, 276, 278, 279, 281 284, 285, 286, 287, 289, 291, 292, 293, 294, 295, 296, 300, 302, 303, 305, 309, 311, 312, 314, 317, 318, 319, 322, 326, 327, 328, 330, 331, 334, 338, 339, 341, 342, 344, 346, 347, 348, 349, 351, 352, 355, 356, and 358; Tyr was changed to Phe at the positions of 27, 50, 80, 160, 182, 197, 244, 251, 260, 307, and 313.

The mutagenesis methods were inverse PCR with paired primers followed by DpnI digestion. The treated product was then transformed into E. coli strain ER2566.

3. Selection of BanII-HF

Selection of BanII-HF was achieved using by comparing the of activity in NEB4 with water with the star activity in Exol buffer and glycerol, using lambda DNA as substrate. Mutants which showed similar or improved activity to WT in water and NEB4, while also showing improved star activity were selected for further testing. These mutants include N106A, Q169A, and E314A. R126A was also chosen because it showed a consistent partial pattern, which we have also shown to be an indicator of high fidelity. After purification, R126A showed the best decrease in star activity. BanII(R126A) is designated BanII-HF.

4. Purification of BanII-HF

Two liters of cell ER2566(pUC19-BanII(R126A), pACYC-BanIIM)) were grown in LB with 100 μg/ml Amp and 33 μg/ml at 30° C. for overnight. The cells were harvested and sonicated in 20 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl. After a centrifugation at 15,000 rpm for 30 minutes, the supernatant was loaded on the 5 ml HiTrap™ Heparin HP column (GE Healthcare, now Pfizer, Inc., Piscataway, N.J.) pre-balanced by the same buffer by syringe injection. The column was then loaded on the system by the following procedure: 48 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl, 100 ml 10 mM Tris-HCl, pH 7.5, 50 mM-1M NaCl linear gradient and followed by a 10 ml 10 mM Tris-HCl, pH 7.5, 1M NaCl step. The eluted fractions were then tested for activity. The fractions with highest activity were further concentrated by Vivaspin® 15R (Vivascience, now Sartorius Vivascience GmbH, Goettingen, Germany). The concentrated BanII-HF was then added an equal volume of glycerol and stored at −20° C.

5. Comparison of BanII-HF and BanII-WT

The FIs of BanII-HF and BanII-WT have been determined separately on dam− lambda DNA in four NEB buffers with diluent A. The result is listed in Table 16 (below).

TABLE 16 Comparison of BanII-HF and BanII-WT BanII-HF BanII-WT Improvement Buffer Activity FI Activity FI Factor NEB1  100% ≧4000  100% 64 ≧64  NEB2   50% ≧2000  100% 64 ≧32  NEB3 12.5% ≧500  12.5% 16 ≧32  NEB4   50% ≧2000  100% 16 ≧125

BanII-HF performed best in NEB1, in which the FI was ≧4000; BanII-WT performed best in NEB1, NEB2 and NEB4, in which the best FI was 64. So the overall improvement factor in NEB1 is ≧4000/64=≧64.

Example 16 Engineering of HF PspGI 1. Expression of PspGI

PspGI was expressed in E. coli transformed with pRRS-PspGIRM which contains PspGI endonuclease and methylase gene. The cells were grown at 30° C. overnight in LB with Amp.

2. Mutagenesis of PspGI-HF

The length of PspGI protein is 272 amino acids. Total 166 AA sites of PspGI protein were initially designed to be mutated into Ala (or Phe). Cys, Asp, Glu, Phe, His, Lys, Met, Asn, Gln, Arg, Ser, Thr, Trp were is mutated to Ala. Try was mutated to Phe. These were: 8, 10, 11, 12, 13, 14, 15, 16, 18, 19, 20, 21, 22, 25, 26, 29, 30, 32, 34, 35, 38, 39, 42, 43, 44, 45, 46, 47, 48, 51, 52, 53, 54, 57, 60, 61, 62, 65, 68, 69, 71, 72, 73, 75, 76, 80, 82, 84, 85, 86, 87, 89, 90, 91, 93, 94, 96, 98, 99, 100, 101, 102, 105, 109, 110, 113, 134, 135, 136, 137, 138, 142, 143, 145, 149, 150, 151, 152, 153, 158, 160, 161, 162, 164, and 165. The mutagenesis methods were inverse PCR with paired primers followed by DpnI digestion. The treated product was then transformed into E. coli strain 2984.

3. Selection of PspGI-HF

Selection of PspGI-HF was achieved using comparison of mutants and WT's activity in NEB4 using pBC4 DNA as substrate. The selection assays of PspGI were performed using pBC4 as substrate in NEB4 (2 h digestion at 69° C.). 11 mutants are found to have more activity in NEB4 than WT: T20A, P52A, Y67F, K68A, R75A, E86A, Q90A, S91A, Q93A, H121A and G172A. PspGI (R75A) has much higher activity than WT in NEB4. Normally the one with highest activity in NEB4 is the one with improved star activity. After several rounds of comparison in different conditions and substrates, PspGI (R75A) was found to be the preferred mutant, retaining high cleavage high activity, but displaying substantially reduced star activity. PspGI (R75A) is designated as PspGI-HF.

4. Purification of PspGI-HF

Two liters of cell E. coli 2984 (pRRS-PspGIRM (R75A)) were grown in LB with 100 μg/ml Amp at 30° C. for overnight. The cells were harvested and sonicated in 20 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl. After a centrifugation at 15,000 rpm for 30 minutes, the supernatant was loaded on the 5 ml HiTrap™ Heparin HP column (GE Healthcare, now Pfizer, Inc., Piscataway, N.J.) pre-balanced by the same buffer by syringe injection. The column was then loaded on the system by the following procedure: 48 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl, 100 ml 10 mM Tris-HCl, pH 7.5, 50 mM-1M NaCl linear gradient and followed by a 10 ml 10 mM Tris-HCl, pH 7.5, 1M NaCl step. The eluted fractions are then test for activity. The fractions with highest activity were further concentrated. The concentrated PspGI-HF was then added same volume of glycerol and stored in the −20° C. condition.

5. Comparison of PspG-HF and PspGI-WT

The FIs of PspG-HF and PspGI-WT have been determined separately on pBC4 DNA in four NEB buffers with diluent A. The result is listed in Table 17 (below).

TABLE 17 Comparison of PspG-HF and PspGI-WT PspGI-HF PspGI-WT Improvement Buffer Activity FI Activity FI Factor NEB1  25% ≧1000 12.5% 1 ≧1000 NEB2 100% ≧4000  100% 4 ≧1000 NEB3 100% ≧4000  100% 8 ≧500  NEB4 100% ≧4000  100% 1 ≧4000

PspGI-HF performed best in at NEB2, NEB3 and NEB4, in which the preferred FI was ≧4000; PspGI-WT performed best in NEB2, NEB3 and NEB4. The preferred FI of PspGI-WT in NEB3 was 8. The overall FI improvement factor was ≧4000/8=≧500.

Example 17 Engineering of HF SpeI 1. Expression of SpeI

SpeI was expressed in E. coli transformed with pRRS-SpeI and pASYX20-SpeIM9, each contains SpeI endonuclease and methylase gene. The cells were grown at 30° C. overnight in LB with Amp and Kan.

2. Mutagenesis of SpeI-HF

All residues Cys, Asp, Glu, Gly, His, Lys, Asn, Pro, Gln, Arg, Ser, Thr were changed to Ala at positions 7, 9, 10, 17, 18, 20, 21, 22, 24, 25, 26, 29, 30, 31, 32, 33, 34, 36, 40, 43, 45, 46, 49, 50, 51, 52, 53, 54, 57, 58, 59, 61, 65, 66, 70, 73, 74, 75, 76, 77, 78, 80, 81, 84, 86, 87, 88, 89, 90, 92, 96, 97, 101, 102, 103, 105, 107, 108, 109, 110, 112, 113, 115, 116, 118, 121, 122, 125, 126, 128, 130, 131, 137, 138, 139, 140, 142, 146, 149, 151, 152, 154, 157, 158, 159, 160, 161, 163, 166, 167, 169, 170, 172, 174, 175, 179, 180, and 182; Tyr was changed to Phe at the positions of 13, 19, 28, 55, 104, 120, 129, and 164.

The mutagenesis methods were inverse PCR with paired primers followed by DpnI digestion. The treated product was then transformed into E. coli strain ER1038.

3. Selection of SpeI-HF

Selection of SpeI-HF was achieved using by comparing the activity of each mutant in NEB4 with water and pXBA DNA that was previously digested with SacI-HF as substrate, to a glycerol reaction with Exol and normal pXba. The SacI-HF digested pXBA allowed for greater clarity when testing mutants for activity compared to WT. The glycerol reaction was is used to compare star activity results. Several mutants showed high cognate activity with a simultaneous decrease in star activity: E059A, P065A, S108A, N172A, K174A, Q179A, G182A, and Y055F. After comparing purified samples, SpeI(P065A) was designated as SpeI-HF.

4. Purification of SpeI-HF

Two liters of cell ER3081(pRRS-SpeIM7(P065A), pSYX20-SpeIM9)) were grown in LB with 100 μg/ml Amp and 33 μg/ml at 30° C. for overnight. The cells were harvested and sonicated in 20 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl. After a centrifugation at 15,000 rpm for 30 minutes, the supernatant was loaded on the 5 ml HiTrap™ Heparin HP column (GE Healthcare, now Pfizer, Inc., Piscataway, N.J.) pre-balanced by the same buffer by syringe injection. The column was then loaded on the system by the following procedure: 48 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl, 100 ml 10 mM Tris-HCl, pH 7.5, 50 mM-1M NaCl linear gradient and followed by a 10 ml 10 mM Tris-HCl, pH 7.5, 1M NaCl step. The eluted fractions were then tested for activity. The fractions with highest activity were further concentrated by Vivaspin® 15R (Vivascience, now Sartorius Vivascience GmbH, Goettingen, Germany). The concentrated SpeI-HF was then added an equal volume of glycerol and stored at −20° C.

5. Comparison of SpeI-HF and SpeI-WT

The FIs of SpeI-HF and SpeI-WT have been determined separately on pXba DNA in four NEB buffers with diluent C. and the result is listed in Table 18 (below).

TABLE 18 Comparison of SpeI-HF and SpeI-WT SpeI-HF SpeI-WT Improvement Buffer Activity FI Activity FI Factor NEB1   50% ≧4000  100% 1000 ≧1000 NEB2 12.5% ≧2000   50%  500 ≧2   NEB3 12.5% ≧2000 12.5% 2000 ≧⅛  NEB4  100% ≧8000   50%  500 ≧2  

SpeI-HF has most activity in NEB4, where the FI is ≧8000; SpeI-WT has most activity in NEB1, where the FI is 1000. So the overall improvement factor is ≧8.

Example 18 Engineering of HF BsmAI 1. Expression of BsmAI

BsmAI was expressed in E. coli transformed with pBAD241-BsmAIR and pACYC-BsmAIM, each contains BsmAI endonuclease and methylase gene. The cells were grown at 37° C. overnight in LB with Amp and Cam and then induced by arabinose for 4 hours.

2. Mutagenesis of BsmAI-HF

Due to the homology among BsaI, BsmBI and BsmAI, amino acids in the region 210-227 of BsmAI were selected to mutate to Ala one at a time because that the high fidelity mutants of BsaI and BsmBI were found in the this similar region.

The mutagenesis methods were inverse PCR with paired primers followed by DpnI digestion. The treated product was then transformed into E. coli strain ER3081.

3. Selection of BsmAI-HF

Selection of BsmAI-HF was achieved using comparison of star activity of mutant BsmAI and WT BsmAI in NEB4 on FX174 DNA as substrate. Two mutants had less star activity than the WT BsmAI: N212A and L213A. Mutant BsmAI(N212A) is designated as BsmAI-HF.

4. Purification of BsmAI-HF

Two liters of cell ER2566(pBAD241-BsmAI(N212A), pACYC184-BsmAIM)) were grown in LB with 100 μg/ml Amp and 33 μg/ml Cam at 37° C. for overnight. Then the cells were induced by arabinose with final concentration of 0.2% for 4 hours. The cells were harvested and sonicated in 20 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl. After a centrifugation at 15,000 rpm for 30 minutes, the supernatant was loaded on the 5 ml HiTrap™ Heparin HP column (GE Healthcare, now Pfizer, Inc., Piscataway, N.J.) pre-balanced by the same buffer by syringe injection. The column was then loaded on the system by the following procedure: 48 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl, 100 ml 10 mM Tris-HCl, pH 7.5, 50 mM-1M NaCl linear gradient and followed by a 10 ml 10 mM Tris-HCl, pH 7.5, 1M NaCl step. The eluted fractions are then test for activity. The fractions with highest activity were further concentrated by Vivaspin® 15R (Vivascience, now Sartorius Vivascience GmbH, Goettingen, Germany). The concentrated BsmAI-HF was then added same volume of glycerol and stored at −20° C.

5. Comparison of BsmAI-HF and BsmAI-WT

The FIs of BsmAI-HF and BsmAI-WT have been determined separately on FX174 DNA in four NEB buffers with diluent B. The result is listed in Table 19 (below).

TABLE 19 Comparison of BsmAI-HF and BsmAI-WT BsmAI-HF BsmAI-WT Improvement Buffer Activity FI Activity FI Factor NEB1  100% ≧4000  50% 120 ≧32 NEB2   50% ≧2000  50% 500 ≧4  NEB3 12.5% ≧500   50% 500 1 NEB4  100% ≧4000 100% 250 ≧8 

BsmAI-HF performed best in NEB1 and NEB4, in which the FI was ≧4000; BsmAI-WT performed best in NEB4, in which the FI was 250. So the overall improvement factor was ≧4000/250=≧16.

Example 19 Engineering of HF BstXI

BstXI recognizes and digests at CCANNNNN/NTGG as described in Example 19 of International Publication No. WO 2009/009797. A mutant BstXI(N65A) was selected as the high fidelity version of the BstXI. A further step to search for better BstXI with less star activity is to mutate N65 to all other amino acid residues. Among those, BstXI(N65T) was found to have less star activity and designated to be BstXI-HF.

The BstXI-HF was expressed in ER2833 (pBAD241-BstXI(N65T), pACYC-BstXIM. The growth and purification methods were performed according to WO/2009/009797.

The following table (Table 20) compares the FIs of BstXI-HF and BstXI WT.

TABLE 20 Comparison of BstXI-HF and BstXI-WT BstXI-HF BstXI-WT Improvement Buffer Activity FI Activity FI Factor NEB1  50% ≧500  6% 4 ≧125 NEB2 100% ≧1000 100% 32 ≧32 NEB3 100% ≧1000 100% 2 ≧500 NEB4 100% ≧1000 100% 32 ≧32

The BstXI-HF had the best activity in NEB2, NEB3 and NEB4, the best FI of BstXI-HF was ≧1000; the WT BstXI had the best activity in NEB2, NEB3 and NEB4. The FI of WT BstXI in NEB2 and NEB4 was 32. So the overall improvement factor was ≧32.

Example 20 Engineering of HF SfiI 1. Expression of SfiI

SfiI was expressed in E. coli transformed with pRRS-SfiIR and pSX33-SfiIM, each contains SfiI endonuclease and methylase gene. The cells were grown at 30° C. overnight in LB with Amp and Kan.

2. Mutagenesis of SfiI-HF

All residues Cys, Asp, Glu, Gly, His, Lys, Asn, Pro, Gln, Arg, Ser, Thr were changed to Ala at positions 7, 9, 11, 12, 14, 15, 17, 18, 19, 20, 22, 23, 26, 29, 30, 32, 33, 34, 36, 37, 40, 41, 42, 45, 46, 47, 48, 49, 55, 56, 58, 59, 63, 66, 67, 69, 71, 72, 73, 76, 79, 81, 82, 84, 87, 88, 89, 90, 91, 94, 95, 100, 102, 104, 105, 106, 107, 108, 109, 110, 111, 113, 114, 115, 116, 118, 120, 122, 124, 125, 126, 127, 128, 129, 130, 133, 135, 137, 140, 141, 145, 146, 148, 149, 150, 153, 156, 157, 158, 162, 166, 167, 169, 170, 172, 173, 174, 176, 177, 179, 180, 185, 187, 188, 190, 192, 193, 194, 196, 197, 198, 199, 200, 201, 202, 205, 207, 208, 209, 210, 211, 213, 214, 215, 218, 220, 224, 225, 227, 228, 231, 233, 235, 236, 238, 240, 242, 243, 244, 246, 247, 248, 249, 251, 252, 254, 255, 257, 258, 259, 261, 262, 263; Tyr is changed to Phe at the positions of 31, 60, 68, 80, 164, 165, 175, 182, 195, 222, 239, and 245.

The mutagenesis methods were inverse PCR with paired primers followed by DpnI digestion. The treated product was then transformed into E. coli strain ER2169.

3. Selection of SfiI-HF

Selection of SfiI-HF was achieved using comparison of activity between mutants and WT in water with NEB Exol buffer and BSA using pXba DNA predigested with EcoRI-HF as substrate. Mutants with similar or greater activity to wild type while also showing a change in star activity in a defined buffer compared to WT were selected. Several mutants are found to have more activity in NEB4: E007A, D011A, E049A, R073A, R0114A, G137A, S210A, and R213A. After purification, P114A proved to have the most significant decrease in star activity. SfiI(R114A) is designated as SfiI-HF.

Also notable were the mutants that increased star activity: N071A, D079A, H162A, R225A, K227A, Y068F, and Y182F. Y068F was previously noted to have different cleavage from WT.

4. Purification of SfiI-HF

Two liters of cell ER2169(pRRS-SfiI(R114A), pSX33-SfiIM)) were grown in LB with 100 μg/ml Amp and 33 μg/ml Kan at 30° C. for overnight. The cells were harvested and sonicated in 20 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl. After a centrifugation at 15,000 rpm for 30 minutes, the supernatant was loaded on the 5 ml HiTrap™ Heparin HP column (GE Healthcare, now Pfizer, Inc., Piscataway, N.J.) pre-balanced by the same buffer by syringe injection. The column was then loaded on the system by the following procedure: 48 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl, 100 ml 10 mM Tris-HCl, pH 7.5, 50 mM-1M NaCl linear gradient and followed by a 10 ml 10 mM Tris-HCl, pH 7.5, 1M NaCl step. The eluted fractions were then tested for activity. The fractions with highest activity were further concentrated by Vivaspin® 15R (Vivascience, now Sartorius Vivascience GmbH, Goettingen, Germany). The concentrated SfiI-HF was then added an equal volume of glycerol and stored at −20° C.

5. Comparison of SfiI-HF and SfiI-WT

The FIs of SfiI-HF and SfiI-WT have been determined separately on pBC4 DNA in four NEB buffers with diluent C. The comparison is shown in FIG. 11, and the result is listed in Table 21 (below).

TABLE 21 Comparison of SfiI-HF and SfiI-HF SfiI-HF SfiI-HF Improvement Buffer Activity FI Activity FI Factor NEB1  50% ≧250 12.5%  64 ≧4 NEB2 12.5%  ≧1000 100% 250 ≧4 NEB3  0.4% ≧32 100% 2000 ≧ 1/64 NEB4 100% ≧8000  25% 64 ≧125

SfiI-HF performed best in NEB4, in which the FI was ≧8000; WT SfiI performed best in NEB3, in which the FI was 2000. The overall improvement factor is ≧8000/2000=≧4.

Example 21 Engineering of HF PmeI 1. Expression of PmeI

PmeI was expressed in E. coli transformed with pRRS-PmeIR and pACYC184-EsaS9IM, each contains PmeI endonuclease and methylase gene. The cells were grown at 37° C. overnight in LB with Amp and Cam.

2. Mutagenesis of PmeI-HF

All residues Cys, Asp, Glu, Gly, His, Lys, Asn, Pro, Gln, Arg, Ser, Thr were changed to Ala at positions 7, 8, 10, 13, 14, 17, 20, 21, 22, 25, 28, 29, 30, 32, 33, 35, 37, 39, 41, 42, 43, 46, 47, 49, 50, 51, 54, 55, 60, 62, 63, 64, 66, 67, 68, 69, 71, 72, 73, 77, 79, 80, 81, 82, 83, 86, 87, 91, 94, 95, 96, 97, 98, 100, 104, 106, 107, 108, 109, 110, 112, 113, 114, 115, 116, 117, 118, 121, 123, 124, 127, 130, 131, 132, 133, 134, 135, 137, 138, 145, 147, 148, 149, 151, 152, 153, 154, 155, 157, 160, 162, 165, 166, 167, 169, 170, 171, 172, 177, 180, 181, 182, 183, 185, 186, 188, 190, 191, 192, 193, 194, 199, 200, 201, 202, 204, 207, 208, 209, 210, 211, 212, 215, 218, 219, 221, 222, 223, 225; Tyr is changed to Phe at the positions of 111, 129, 146, and 161.

The mutagenesis methods were inverse PCR with paired primers followed by DpnI digestion. The treated product was then transformed into E. coli strain ER2426.

3. Selection of PmeI-HF

Selection of PmeI-HF was achieved using comparison of activity between WT and mutants in water NEB4 using lambda DNA as substrate with the same mutants in glycerol with NEB Thermopol buffer and pXba as a substrate. The testing of mutants and WT PmeI in water on lambda DNA allowed for a reference of cognate activity, and with similar or more activity than WT in NEB4 were selected. Mutants with acceptable activity were then rejected if they showed no change in star activity when tested under glycerol conditions with Thermopol buffer and pXba. Several mutants were shown to have differences in star activity: P079A, E086A, H096A, and E218A. PmeI(E086A) is designated as PmeI-HF.

4. Purification of PmeI-HF

Two liters of cell ER2426(pRRS-PmeI(P154A), pACYC184-EsaS91M)) were grown in LB with 100 μg/ml Amp and 33 μg/ml Cam at 37° C. overnight. The cells were harvested and sonicated in 20 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl. After a centrifugation at 15,000 rpm for 30 minutes, the supernatant was loaded on the 5 ml HiTrap™ Heparin HP column (GE Healthcare, now Pfizer, Inc., Piscataway, N.J.) pre-balanced by the same buffer by syringe injection. The column was then loaded on the system by the following procedure: 48 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl, 100 ml 10 mM Tris-HCl, pH 7.5, 50 mM-1M NaCl linear gradient and followed by a 10 ml 10 mM Tris-HCl, pH 7.5, 1M NaCl step. The eluted fractions were then tested for activity. The fractions with highest activity were further concentrated by Vivaspin® 15R (Vivascience, now Sartorius Vivascience GmbH, Goettingen, Germany). The concentrated PmeI-HF was then added an equal volume of glycerol and stored at −20° C.

5. Comparison of PmeI-HF and PmeI-WT

The FIs of PmeI-HF and PmeI-WT have been determined separately on pXba DNA in four NEB buffers with diluent A. The result is listed in Table 22 (below).

TABLE 22 Comparison of PmeI-HF and PmeI-WT PmeI-HF PmeI-WT Improvement Buffer Activity FI Activity FI Factor NEB1 12.5%  ≧2000 100% 250 ≧64 NEB2 6.3% ≧500 100% 250 ≧500 NEB3 0.4% ≧32  50% 120 ≧125 NEB4 100%  ≧8000  25% 64 ≧500

PmeI-HF performed best in NEB4, in which the FI was ≧8000; PmeI-WT performed best in NEB1 and NEB2, in which the FI was 250. The overall improvement factor is ≧8000/250=≧16.

Example 22 Engineering of HF SmaI 1. Expression of SmaI

SmaI was expressed in E. coli transformed with pRRS-SmaIR and pSYX20-SmaIM, each contains SmaI endonuclease and methylase gene. The cells were grown at 37° C. overnight in LB with Amp and Kan.

2. Mutagenesis of SmaI-HF

All residues Cys, Asp, Glu, Gly, His, Lys, Asn, Pro, Gln, Arg, Ser, Thr were changed to Ala; all Tyr were changed to Phe.

The mutagenesis methods were inverse PCR with paired primers followed by DpnI digestion. The treated product was then transformed into E. coli strain ER2428.

3. Selection of SmaI-HF

Selection of SmaI-HF was achieved using comparison of activity in water NEB4 using pXba DNA as substrate with a star-activity producing glycerol condition with NEB Standard Taq buffer. Mutants which showed changes in star activity in the designated buffer while retaining similar or high cognate activity to WT were selected. Several mutants were found: E32R, S081A, G132A and a double-mutant F60L/S61R. SmaI(F60L/S61R) is designated as SmaI-HF.

4. Purification of SmaI-HF

Two liters of cell ER2428(pRRS-SmaI(F60L/S61R), pSYX20-SmaIM)) were grown in LB with 100 μg/ml Amp and 33 μg/ml Kan at 37° C. overnight. The cells were harvested and sonicated in 20 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl. After a centrifugation at 15,000 rpm for 30 minutes, the supernatant was loaded on the 5 ml HiTrap™ Heparin HP column (GE Healthcare, now Pfizer, Inc., Piscataway, N.J.) pre-balanced by the same buffer by syringe injection. The column was then loaded on the system by the following procedure: 48 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl, 100 ml 10 mM Tris-HCl, pH 7.5, 50 mM-1M NaCl linear gradient and followed by a 10 ml 10 mM Tris-HCl, pH 7.5, 1M NaCl step. The eluted fractions were then tested for activity. The fractions with highest activity were further concentrated by Vivaspin® 15R (Vivascience, now Sartorius Vivascience GmbH, Goettingen, Germany). The concentrated SmaI-HF was then added an equal volume of glycerol and stored at −20° C.

5. Comparison of SmaI-HF and SmaI-WT

The FIs of SmaI-HF and WT SmaI have been determined separately on pXba DNA in four NEB buffers with diluent A. The comparison is shown in FIG. 12, and the result is listed in Table 23 (below).

TABLE 23 Comparison of SmaI-HF and SmaI-WT SmaI-HF SmaI-WT Improvement Buffer Activity FI Activity FI Factor NEB1 0.2% ≧2000  3% ≧16 ND NEB2 3.2% ≧32000 12.5%  ≧64 ND NEB3 0.0032%   ≧32  0.8% ≧8 ND NEB4 100%  ≧256000 100% 64 ≧4000 ND: Not determinable

SmaI-HF performed best in NEB4, in which the FI was ≧256000; SmaI-WT performed best in NEB2 and NEB4, in which the FI was 64. The overall improvement factor is ≧256000/64=≧4000.

Example 23 Engineering of High Fidelity AatII 1. Expression of AatII

AatII was expressed in E. coli transformed with pRRS-AatIIR and pACYC184-AatIIM, each contains AatII endonuclease and methylase gene. The cells were grown at 37° C. overnight in LB with Amp and Cam.

2. Mutagenesis of AatII-HF

All residues Cys, Asp, Glu, Gly, His, Lys, Asn, Pro, Gln, Arg, Ser, Thr were changed to Ala at positions 8, 9, 11, 12, 13, 16, 17, 18, 20, 22, 26, 29, 32, 33, 35, 36, 37, 38, 40, 43, 45, 46, 49, 52, 53, 54, 56, 57, 58, 60, 61, 62, 64, 65, 69, 70, 71, 72, 73, 74, 75, 77, 79, 80, 83, 84, 86, 87, 90, 92, 93, 94, 95, 97, 99, 100, 103, 104, 106, 107, 111, 113, 114, 117, 121, 123, 124, 125, 126, 128, 129, 131, 132, 133, 135, 136, 140, 141, 143, 144, 145, 146, 148, 149, 150, 151, 153, 155, 156, 157, 160, 164, 165, 167, 169, 171, 172, 173, 174, 175, 176, 177, 179, 181, 182, 186, 189, 191, 192, 193, 194, 196, 198, 200, 201, 203, 204, 205, 206, 207, 208, 210, 211, 213, 214, 216, 217, 219, 220, 221, 222, 226, 228, 230, 231, 233, 235, 236, 237, 238, 240, 241, 244, 247, 248, 249, 250, 251, 252, 253, 256, 262, 264, 265, 266, 268, 269, 272, 273, 275, 280, 281, 282, 283, 286, 298, 292, 293, 295, 296, 297, 298, 301, 302, 308, 309, 311, 312, 313, 314, 315, 317, 319, 321, 325, 327, 329, 330, 333, 334, 335, 336; Tyr was changed to Phe at the positions of 82, 89, 98, 112, 232, 305, and 306.

The mutagenesis methods were inverse PCR with paired primers followed by DpnI digestion. The treated product was then transformed into E. coli strain ER2426.

3. Selection of AatII-HF

Selection of AatII-HF was achieved using comparison of activity in NEB4 in water to NEB Exol buffer in glycerol using pXba DNA as substrate. Mutants which showed changes in star activity under the glycerol conditions were chosen for further testing as long as they had similar or greater activity than WT under normal conditions in water. Several mutants were chosen for further testing after the initial screen: G013A, G016A, K018A, P052A, R053A, K070A, E071A, D072A, G073A, S84A, E086A, R090A, K094A, R095A, P099A, P103A, K113A, N135A, S151A, P157A, G173A, T204A, S206A, K207A, E233A, N235A, E237A, S238A, D241A, K295A, S301A, and S302A. AatII(N235A) is designated as AatII-HF.

4. Purification of AatII-HF

Two liters of cell ER2426(pRRS-AatII(N235A), pACYC184-AatIIM)) were grown in LB with 100 μg/ml Amp and 33 μg/ml Cam at 37° C. overnight. The cells were harvested and sonicated in 20 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl. After a centrifugation at 15,000 rpm for 30 minutes, the supernatant was loaded on the 5 ml HiTrap™ Heparin HP column (GE Healthcare, now Pfizer, Inc., Piscataway, N.J.) pre-balanced by the same buffer by syringe injection. The column was then loaded on the system by the following procedure: 48 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl, 100 ml 10 mM Tris-HCl, pH 7.5, 50 mM-1M NaCl linear gradient and followed by a 10 ml 10 mM Tris-HCl, pH 7.5, 1M NaCl step. The eluted fractions were then tested for activity. The fractions with highest activity were further concentrated by Vivaspin® 15R (Vivascience, now Sartorius Vivascience GmbH, Goettingen, Germany). The concentrated AatII-HF was then added an equal volume of glycerol and stored at −20° C.

5. Comparison of AatII-HF and AatII-WT

The FIs of AatII-HF and WT AatII have been determined separately on pBR322 DNA in four NEB buffers with diluent A. The result is listed in Table 24 (below).

TABLE 24 Comparison of AatII-HF and AatII-WT AatII-HF AatII-WT Improvement Buffer Activity FI Activity FI Factor NEB1 NC NC  3% 32 ND NEB2 NC NC 100%  ¼ ND NEB3 NC NC NC NC ND NEB4 100% ≧1000 50% 16 ≧64 NC: Not completable; ND: Not determinable

AatII-HF performed best in NEB4, in which the FI was ≧1000; WT AatII performed best in NEB2, in which the FI was ¼. The overall improvement factor is ≧1000/¼=≧4000.

Example 24 Engineering of HF ApoI 1. Expression of ApoI

ApoI was expressed in E. coli transformed with pRRS-ApoIR and pACYC184-ApoIM, each contains ApoI endonuclease and methylase gene. The cells were grown at 37° C. overnight in LB with Amp and Cam.

2. Mutagenesis of ApoI-HF

All residues Cys, Asp, Glu, Gly, His, Lys, Asn, Pro, Gln, and Arg, were changed to Ala at positions 8, 9, 10, 11, 13, 14, 17, 18, 19, 20, 21, 22, 23, 24, 26, 28, 29, 33, 35, 36, 37, 39, 41, 43, 47, 48, 49, 50, 51, 56, 57, 60, 62, 63, 64, 66, 67, 69, 71, 72, 73, 75, 76, 77, 80, 81, 82, 83, 84, 87, 92, 93, 94, 95, 96, 97, 102, 103, 105, 106, 107, 108, 109, 110, 111, 113, 115, 116, 117, 119, 120, 121, 124, 125, 128, 129, 131, 132, 133, 136, 137, 143, 144, 145, 148, 153, 155, 157, 159, 160, 161, 162, 163, 166, 167, 169, 170, 175, 176, 178, 179, 181, 184, 185, 186, 187, 188, 189, 192, 193, 194, 195, 199, 201, 202, 204, 206, 207, 209, 210, 214, 216, 217, 218, 221, 226, 227, 229, and 230.

The mutagenesis methods were inverse PCR with paired primers followed by DpnI digestion. The treated product was then transformed into E. coli strain ER2426.

3. Selection of ApoI-HF

Selection of ApoI-HF was achieved using comparison of activity in NEB3 and NEB4 using lambda DNA as substrate. Mutants with more activity than WT in NEB4 were selected as increased activity in NEB4 is an indicator of improved fidelity. The following mutants are found to have is more activity in NEB4: S64A, S80A, S162A, T77A/T96A and N178A. ApoI(T77A/T96A) is designated as ApoI-HF.

4. Purification of ApoI-HF

Two liters of cell ER2426(pRRS-ApoI(T77A/T96A), pACYC184-ApoIM)) were grown in LB with 100 μg/ml Amp and 33 μg/ml Cam at 37° C. overnight, induced with 0.5 mM ITPG after 8 hours of growth. The cells were harvested and sonicated in 20 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl. After a centrifugation at 15,000 rpm for 30 minutes, the supernatant was loaded on the 5 ml HiTrap™ Heparin HP column (GE Healthcare, now Pfizer, Inc., Piscataway, N.J.) pre-balanced by the same buffer by syringe injection. The column was then loaded on the system by the following procedure: 48 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl, 100 ml 10 mM Tris-HCl, pH 7.5, 50 mM-1M NaCl linear gradient and followed by a 10 ml 10 mM Tris-HCl, pH 7.5, 1M NaCl step. The eluted fractions were then tested for activity. The fractions with highest activity were further concentrated by Vivaspin® 15R (Vivascience, now Sartorius Vivascience GmbH, Goettingen, Germany). The concentrated ApoI-HF was then added an equal volume of glycerol and stored at −20° C.

5. Comparison of ApoI-HF and ApoI-WT

The FIs of ApoI-HF and ApoI-WT have been determined separately on pXba DNA in four NEB buffers with diluent A. The result is listed in Table 24 (below).

TABLE 24 Comparison of ApoI-HF and ApoI-WT ApoI-HF ApoI-WT Improvement Buffer Activity FI Activity FI Factor NEB1 50% ≧2000  25% 120 ≧16 NEB2 100%  ≧4000 100% 32 ≧125 NEB3 25% ≧1000 100% 64 ≧16 NEB4 50% ≧2000  50% 32 ≧64

ApoI-HF performed best in NEB2, in which the FI was ≧4000; WT ApoI performed best in NEB2 and NEB3, in which the best FI was 64. The overall improvement factor is ≧4000/64=≧64.

Example 25 Engineering of High Fidelity BsmBI

BsmBI recognizes and digests at CGTCTCN1/N5 as described in Example 23 of International Publication No. WO 2009/009797. A mutant BsmBI(R232A) was selected as the high fidelity version of the BsmBI. Further characterization of this mutant revealed that though the performance of BsmBI(R232A) on one hour scale is excellent, it did not perform well in the overnight digestion. While searching for more mutants, BsmBI(W238A) was found to be excellent in both one hour and overnight reaction, and designated to be BsmBI-HF (FIG. 13).

The BsmBI-HF was expressed in ER3081 (pBAD241-BsmBIR(W238A)/pACYC-BsmAIM). The growth and purification methods were performed according to WO/2009/009797.

The following table (Table 26) compares the FIs of BsmBI-HF and BsmBI-WT.

TABLE 26 Comparison of BsmBI-HF and BsmBI-WT BsmBI-HF BsmBI-WT Improvement Buffer Activity FI Activity FI Factor NEB1 50% 32 12.5%  1 32 NEB2 50% 120 50% 8 25 NEB3 12.5%  250 100%  120 2 NEB4 100%  250 25% 4 64

The BsmBI-HF had the best activity in NEB4, the FI of BsmBI-HF in NEB4 was 250; the BsmBI-WT had the best activity in NEB3. The FI of WT BsmBI in NEB2 was 120. So the overall improvement factor was 2.

Example 26 Engineering of HF BmtI 1. Expression of BmtI

BmtI was expressed in E. coli transformed with pACYC-BmtIM and placzz1-BmtIR. pACYC is a low copy compatible plasmid. The cells were grown at 37° C. overnight in LB with Amp and Cam.

2. Mutagenesis of BmtI-HF

The point mutagenesis of the selected mutations was done by inverse PCR. 150 amino acid mutations were made in BmtI as follows. Cys, Asp, Glu, Phe, His, Lys, Met, Asn, Gln, Arg, Ser, Thr, Trp were mutated to Ala. Try was mutated to Phe. These were: 5, 9, 11, 12, 16, 19, 20, 23, 24, 25, 26, 27, 30, 32, 33, 34, 35, 36, 39, 45, 46, 49, 50, 51, 53, 56, 58, 59, 60, 63, 65, 69, 71, 72, 73, 74, 75, 76, 78, 79, 80, 81, 83, 85, 86, 88, 89, 90, 92, 93, 94, 95, 97, 98, 99, 101, 104, 105, 106, 108, 110, 111, 112, 113, 116, 118, 119, 120, 121, 122, 124, 128, 129, 131, 132, 133, 134, 136, 138, 139, 140, 141, 142, 144, 145, 146, 147, 148, 150, 151, 152, 154, 156, 157, 161, 162, 163, 165, 166, 167, 168, 169, 171, 172, 173, 175, 178, 179, 180, 181, 185, 186, 189, 190, 191, 193, 194, 195, 196, 199, 200, 201, 202, 203, 204, 205, 206, 207, 208, 210, 211, 213, 214, 216, 217, 218, 219, 220, 221, 222, 226, 228, 229, 230, 231, 234, 236, 237, 238, 239 and 241. The mutagenesis methods were inverse PCR with paired primers followed by DpnI digestion. The treated product was then transformed into E. coli strain 3081.

3. Selection of BmtI-HF

Four colonies of each mutation were grown up in LB with Amp and Cam at 37° C. overnight. The standard cognate and star activity assays of BmtI were performed using pBC4 in ExoI buffer and 10% DMSO.

The mutants S50A, Y81F, N93A and W207A were picked out in screening assays. After several rounds of comparison in different conditions and substrates, S50A was found to be the preferred mutant, retaining high canonical enzyme activity, but displaying substantially reduced star activity. BmtI(S50A) was labeled as BmtI-HF.

4. Purification of BmtI-HF

Two liters of cell E. coli 3081 (placzz1-BmtIR(S50A), pACYC-BmtIM) were grown in LB with 100 μg/ml Amp and 30 μg/ml Cam at 37° C. for overnight. The cells were harvested and sonicated in 20 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl. After a centrifugation at 15,000 rpm for 30 minutes, the supernatant was loaded on the 5 ml HiTrap™ Heparin HP column (GE Healthcare, now Pfizer, Inc., Piscataway, N.J.) pre-balanced by the same buffer by syringe injection. The column was then loaded on the system by the following procedure: 48 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl, 100 ml 10 mM Tris-HCl, pH 7.5, 50 mM-1M NaCl linear gradient and followed by a 10 ml 10 mM Tris-HCl, pH 7.5, 1M NaCl step. The eluted fractions are then test for activity. The fractions with highest activity were further concentrated. The concentrated BmtI-HF was then added same volume of glycerol and stored at −20° C.

5. Comparison of BmtI-HF and BmtI-WT

BmtI-HF was 2-fold serial diluted with A and reacted on pXba. The result is shown in Table 27.

TABLE 27 Comparison of BmtI-HF and BmtI-WT BmtI-HF BmtI-WT Improvement Buffer Activity FI Activity FI Factor NEB1 25% ≧256000  50% 32 ≧8000 NEB2 25% ≧256000 100% 16 ≧16000 NEB3 0.2%  ≧2000  6.3% 32 ≧64 NEB4 100%  ≧1000000 100% 16 ≧62500

BmtI-HF performed best in NEB4, in which the preferred FI was ≧1000000; BmtI-WT performed best in NEB2 and NEB4, where the FI was 16. The overall FI improvement factor was ≧1000000/16=≧62500

Example 27 Engineering of HF BstNI 1. Expression of BstNI

BstNI was expressed in E. coli transformed with pBAD241-BstNIR and pACYC184-BstNIM, each contains BstNI endonuclease and methylase gene. The cells were grown at 37° C. overnight in LB with Amp and Cam, diluted to 1/10 with LB and then induced by arabinose for 4 hours.

2. Mutagenesis and Selection of BstNI-HF

During the experiment of creating a series mutations of BstNI, BstNI(G26N) was found to have less star activity than the WT BstNI. To searching for better BstNI mutants with even less star activity, G26 was is mutated to all other amino acids. Among all these mutants, BstNI(G26T) has the least star activity and is designated as BstNI-HF.

3. Purification of BstNI-HF

Two liters of cell ER2833(pBAD241-BstNI(G26T), pACYC184-BstNIM) were grown in LB with 100 μg/ml Amp and 33 μg/ml Cam at 37° C. for overnight. Then the cells were diluted 1 to 10 with LB and then induced by arabinose with final concentration of 0.2% for 4 hours. The cells were harvested and sonicated in 20 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl. After a centrifugation at 15,000 rpm for 30 minutes, the supernatant was loaded on the 5 ml HiTrap™ Heparin HP column (GE Healthcare, now Pfizer, Inc., Piscataway, N.J.) pre-balanced by the same buffer by syringe injection. The column was then loaded on the system by the following procedure: 48 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl, 100 ml 10 mM Tris-HCl, pH 7.5, 50 mM-1M NaCl linear gradient and followed by a 10 ml 10 mM Tris-HCl, pH 7.5, 1M NaCl step. The eluted fractions are then test for activity. The fractions with highest activity were further concentrated by Vivaspin® 15R (Vivascience, now Sartorius Vivascience GmbH, Goettingen, Germany). The concentrated BstNI-HF was then added same volume of glycerol and stored at −20° C.

4. Comparison of BstNI-HF and WT BstNI

The FIs of BstNI-HF and WT BstNI have been determined separately on pBR322 DNA in four NEB buffers with diluent A. The comparison is shown in FIG. 14, and the result is listed in Table 28 (below).

TABLE 28 Comparison of BstNI-HF and BstNI-WT BstNI-HF BstNI-WT Improvement Buffer Activity FI Activity FI Factor NEB1  50% ≧120  50% 8 ≧16 NEB2 100% ≧500 100% 64 8 NEB3  25% ≧120 100% 250 ≧⅛ NEB4 100% 500  50% 4 ≧32

BstNI-HF performed best in NEB2 and NEB4, in which the best FI was ≧500; BstNI-WT performed best in NEB2 and NEB3, in which the best FI was 250. So the overall improvement factor was ≧500/250=≧2.

Example 28 Engineering of HF MluI 1. Expression of MluI

MluI was expressed in E. coli transformed with pUC19-MluIR and pACYC184-MluIM, each contains MluI endonuclease and methylase gene. The cells were grown at 30° C. overnight in LB with Amp and Cam.

2. Mutagenesis of MluI-HF

All residues Cys, Asp, Glu, Gly, His, Lys, Asn, Pro, Gln, Arg, Ser, Thr were changed to Ala at positions 7, 8, 10, 11, 13, 16, 21, 23, 24, 26, 27, 30, 31, 33, 34, 35, 36, 37, 39, 42, 44, 48, 50, 51, 54, 57, 59, 60, 61, 67, 68, 71, 72, 74, 75, 78, 79, 81, 83, 84, 85, 86, 89, 90, 93, 94, 95, 97, 99, 101, 102, 104, 106, 108, 111, 112, 114, 116, 117, 119, 120, 121, 123, 125, 128, 130, 131, 132, 134, 136, 137, 139, 140, 141, 142, 144, 145, 146, 148, 152, 154, 155, 156, 157, 159, 161, 163, 165, 166, 170, 172, 173, 174, 176, 177, 179, 180, 181, 182, 183, 184, 186, 189, 192, 195, 196, 197, 200, 206, 207, 208, 210, 211, 214, 216, 218, 219, 220, 221, 223, 227, 228, 230, 232, 233, 234, 236, 237, 238, 240, 243, 244, 247, 249, 255, 256, 257, 258, 261, 263, 264, 265, 266, 269; Tyr was changed to Phe at the positions of 14, 28, 47, 53, 77, 107, 175, 198, 217, 239, and 248.

The mutagenesis methods were inverse PCR with paired primers is followed by DpnI digestion. The treated product was then transformed into E. coli strain ER1582.

3. Selection of MluI-HF

Selection of MluI-HF was achieved using comparison of activity in NEB3 and NEB4 using lambda DNA as substrate. Mutants with more activity than WT in NEB4 were selected as increased activity in NEB4 is an indicator of improved fidelity. The only mutant found to fit our criteria was E112A/R132A; MluI(E112A/R132A) is designated as MluI-HF.

4. Purification of MluI-HF

Two liters of cell ER1582(pUC19-MluI(E112A/R132A), pACYC184-MluIM)) were grown in LB with 100 μg/ml Amp and 33 μg/ml Cam at 30° C. overnight. The cells were harvested and sonicated in 20 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl. After a centrifugation at 15,000 rpm for 30 minutes, the supernatant was loaded on the 5 ml HiTrap™ Heparin HP column (GE Healthcare, now Pfizer, Inc., Piscataway, N.J.) pre-balanced by the same buffer by syringe injection. The column was then loaded on the system by the following procedure: 48 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl, 100 ml 10 mM Tris-HCl, pH 7.5, 50 mM-1M NaCl linear gradient and followed by a 10 ml 10 mM Tris-HCl, pH 7.5, 1M NaCl step. The eluted fractions were then tested for activity. The fractions with highest activity were further concentrated by Vivaspin® 15R (Vivascience, now Sartorius Vivascience GmbH, Goettingen, Germany). The concentrated MluI-HF was then added an equal volume of glycerol and stored at −20° C.

5. Comparison of MluI-HF and MluI-WT

The FIs of MluI-HF and WT MluI have been determined separately on lambda DNA in four NEB buffers with diluent A. The comparison is shown in FIG. 15, and the result is listed in Table 29 (below).

TABLE 29 Comparison of MluI-HF and MluI-WT MluI-HF MluI-WT Improvement Buffer Activity FI Activity FI Factor NEB1  50% ≧16000 25% 500 ≧32 NEB2 100% ≧32000 6.3%  16 ≧200 NEB3  6.3% ≧2000 100%  2000 ≧1 NEB4 100% ≧32000 25% 32 ≧1000

MluI-HF performed best in NEB2 and NEB4, in which the FI was ≧32000; MluI-WT performed best in NEB3, in which the FI was 2000. The overall improvement factor is ≧32000/2000=≧16.

Example 29 Engineering of HF BanI 1. Expression of BanI

BanI was expressed in E. coli transformed with pUC19-BanIR and pACYC184-BanIM, each contains BanI endonuclease and methylase gene. The cells were grown at 37° C. overnight in LB with Amp and Cam.

2. Mutagenesis of BanI-HF

All residues Cys, Asp, Glu, Gly, His, Lys, Asn, Pro, Gln, Arg, Ser, Thr were changed to Ala at positions 7, 8, 9, 11, 12, 14, 15, 16, 19, 22, 23, 27, 28, 29, 30, 31, 32, 33, 36, 37, 40, 41, 42, 43, 47, 50, 52, 53, 54, 55, 56, 58, 61, 64, 66, 67, 69, 70, 71, 75, 76, 81, 82, 84, 85, 86, 87, 89, 90, 92, 93, 94, 96, 97, 100, 103, 105, 106, 107, 109, 110, 111, 112, 114, 115, 117, 121, 122, 123, 124, 126, 130, 131, 133, 135, 136, 138, 139, 140, 141, 143, 145, 146, 148, 150, 151, 152, 154, 156, 157, 160, 161, 169, 171, 174, 175, 176, 178, 179, 182, 183, 185, 187, 188, 191, 192, 193, 194, 195, 197, 198, 201, 202, 203, 208, 209, 211, 212, 213, 215, 217, 218, 220, 221, 224, 225, 226, 229, 232, 233, 234, 236, 237, 238, 240, 242, 243, 244, 245, 246, 248, 249, 251, 252, 253, 254, 255, 256, 257, 259, 260, 262, 266, 267, 268, 269, 270, 271, 275, 277, 279, 281, 282, 283, 284, 285, 287, 288, 289, 291, 292, 294, 296, 298, 301, 302, 303, 304, 305, 312, 313, 315, 316, 318, 319, 320, 321, 324, 325, 328, 329, 330, 331, 333, 337, 338, 339, 340, 342, 346; Tyr was changed to Phe at the positions of 104, 125, 127, 156, 159, 204, 239, 297, 306, and 336.

The mutagenesis methods were inverse PCR with paired primers followed by DpnI digestion. The treated product was then transformed into E. coli strain ER2683.

3. Selection of BanI-HF

Selection of BanI-HF was achieved using comparison of activity in water and NEB4 versus glycerol and NEB Exol buffer using lambda DNA as substrate. Mutants with as much or more activity than WT in NEB4 were selected if they also showed a change in star activity when tested under glycerol conditions. Another indicator used in selecting these mutants was the fact that removing star activity creates a slow site in cognate cleavage. Numerous mutants were found to have changes in star activity and the resulting slow site: N016A, S33A, P36A, H76A, P87A, N89A, R90A, T138A, K141A, K143A, Q221A, Q224A, N253A, Q292A, R296A, T152I, G326A, and T324A. BanI(Q292A) is designated as BanI-HF.

4. Purification of BanI-HF

Two liters of cell ER2683(pUC19-BanI(P154A), pACYC184-BanIM)) were grown in LB with 100 μg/ml Amp and 33 μg/ml Cam at 37° C. overnight. The cells were harvested and sonicated in 20 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl. After a centrifugation at 15,000 rpm for 30 minutes, the supernatant was loaded on the 5 ml HiTrap™ Heparin HP column (GE Healthcare, now Pfizer, Inc., Piscataway, N.J.) pre-balanced by is the same buffer by syringe injection. The column was then loaded on the system by the following procedure: 48 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl, 100 ml 10 mM Tris-HCl, pH 7.5, 50 mM-1M NaCl linear gradient and followed by a 10 ml 10 mM Tris-HCl, pH 7.5, 1M NaCl step. The eluted fractions were then tested for activity. The fractions with highest activity were further concentrated by Vivaspin® 15R (Vivascience, now Sartorius Vivascience GmbH, Goettingen, Germany). The concentrated BanI-HF was then added an equal volume of glycerol and stored at −20° C.

5. Comparison of BanI-HF and BanI-WT

The FIs of BanI-HF and WT BanI have been determined separately on lambda DNA in four NEB buffers with diluent A. The result is listed in Table 30 (below).

TABLE 30 Comparison of BanI-HF and BanI-WT BanI-HF BanI-WT Improvement Buffer Activity FI Activity FI Factor NEB1  50% ≧1000 25% 4 ≧250 NEB2 12.5%  ≧250 25% 4 ≧63 NEB3  0.4% ≧8 6.3%  2 ≧4 NEB4 100% ≧2000 100%  16 ≧125

BanI-HF performed best in NEB4, in which the FI was ≧2000; WT BanI also performed best in NEB4, but the FI was only 16. The overall improvement factor is ≧2000/16=≧125.

Example 30 Engineering of HF KasI 1. Expression of KasI

KasI was expressed in E. coli transformed with placZZ-KasIR and pACY-SfoIM, each contains KasI endonuclease and methylase gene. The cells were grown at 30° C. overnight in LB with Amp and Cam.

2. Mutagenesis of KasI-HF

All residues Cys, Asp, Glu, Gly, His, Lys, Asn, Pro, Gln, Arg, Ser, Thr were changed to Ala at positions 7, 8, 9, 11, 13, 14, 17, 18, 21, 24, 26, 28, 29, 31, 32, 33, 34, 36, 37, 39, 42, 43, 44, 47, 48, 51, 52, 54, 55, 56, 58, 60, 62, 63, 64, 65, 66, 69, 70, 73, 76, 77, 78, 79, 83, 85, 86, 88, 89, 90, 91, 92, 93, 94, 98, 100, 101, 102, 103, 104, 108, 110, 111, 114, 115, 116, 117, 118, 119, 122, 123, 124, 125, 126, 128, 129, 134, 137, 138, 139, 140, 142, 143, 144, 145, 146, 149, 150, 152, 153, 154, 156, 158, 161, 162, 163, 164, 165, 167, 168, 173, 177, 178, 180, 181, 182\, 184, 185, 188, 189, 190, 191, 192, 195, 197, 198, 200, 202, 203, 204, 210, 211, 212, 214, 215, 216, 217, 218, 219, 220, 221, 222, 223, 225, 226, 228, 229, 231, 234, 237, 238, 241, 243, 244, 245, 246, 248, 251, 253, 255, 257, 258, 259, 260, 261, 263, 264, 265, 266, 269, 270, 271, 274, 275, 276, 277, and 278; Tyr was changed to Phe at the positions of 19, 41, 74, 80, 95, 207, and 256.

The mutagenesis methods were inverse PCR with paired primers followed by DpnI digestion. The treated product was then transformed into E. coli strain ER2683.

3. Selection of KasI-HF

Selection of KasI-HF was achieved using comparison of activity in NEB3 and NEB4 using pBR322 DNA as substrate. Mutants with more activity than WT in NEB4 were selected as increased activity in NEB4 is an indicator of improved fidelity. The following mutants were found to have more activity in NEB4: K024A, P214A, E146A, N251A and Y095F. KasI(N251A) is designated as KasI-HF.

4. Purification of KasI-HF

Two liters of cell ER2683(pLacZZ-KasI(M251A), pACYC-SfoIM)) were grown in LB with 100 μg/ml Amp and 33 μg/ml Cam at 30° C. overnight. The cells were harvested and sonicated in 20 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl. After a centrifugation at 15,000 rpm for 30 minutes, the supernatant was loaded on the 5 ml HiTrap™ Heparin HP column (GE Healthcare, now Pfizer, Inc., Piscataway, N.J.) pre-balanced by the same buffer by syringe injection. The column was then loaded on the system by the following procedure: 48 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl, 100 ml 10 mM Tris-HCl, pH 7.5, 50 mM-1M NaCl linear gradient and followed by a 10 ml 10 mM Tris-HCl, pH 7.5, 1M NaCl step. The eluted fractions were then tested for activity. The fractions with highest activity were further concentrated by Vivaspin® 15R (Vivascience, now Sartorius Vivascience GmbH, Goettingen, Germany). The concentrated KasI-HF was then added an equal volume of glycerol and stored at −20° C.

5. Comparison of KasI-HF and KasI-WT

The FIs of KasI-HF and KasI-WT have been determined separately on pBR322 DNA in four NEB buffers with diluent B. The result is listed in Table 31 (below).

TABLE 31 Comparison of KasI-HF and KasI-WT KasI-HF KasI-WT Improvement Buffer Activity FI Activity FI Factor NEB1  50% ≧8000 100% 1 ≧8000 NEB2 100% ≧16000 100% 8 ≧2000 NEB3 12.5%  ≧2000 100% 8 ≧250 NEB4 100% ≧16000 100% 4 ≧4000

KasI-HF performed best in NEB2 and NEB4, in which the FI is ≧16000; KasI-WT performed same in all buffers, in which the best FI is 8. The overall improvement factor is ≧16000/8=≧2000.

Example 31 Engineering of HF NruI 1. Expression of NruI

NruI was expressed in E. coli transformed with pUC19-NruIR and pACYC-Sbo13IM, each contains NruI endonuclease and methylase gene. The cells were grown at 37° C. overnight in LB with Amp and Cam.

2. Mutagenesis of NruI-HF

All residues Cys, Asp, Glu, Gly, His, Lys, Asn, Pro, Gln, Arg, Ser, Thr were changed to Ala at positions 8, 10, 12, 13, 15, 16, 19, 20, 21, 22, 23, 25, 26, 30, 34, 36, 38, 39, 44, 45, 46, 47, 49, 50, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 68, 70, 71, 72, 73, 75, 77, 79, 80, 82, 83, 84, 85, 87, 89, 90, 91, 92, 93, 95, 96, 97, 99, 101, 103, 104, 106, 107, 112, 113, 114, 115, 117, 118, 119, 124, 125, 127, 132, 134, 137, 138, 139, 141, 146, 147, 148, 149, 152, 154, 155, 157, 158, 159, 162, 163, 165, 166, 168, 169, 170, 171, 174, 175, 177, 178, 180, 182, 184, 186, 188, 189, 190, 191, 193, 196, 197, 200, 201, 202, 204, 205, 206, 207, 208, 209, 211, and 213; Tyr was changed to Phe at the positions of 11, 31, 52, 69, 98, 64, and 187.

The mutagenesis methods were inverse PCR with paired primers followed by DpnI digestion. The treated product was then transformed into E. coli strain ER2683.

3. Selection of NruI-HF

Selection of NruI-HF was achieved using comparison of activity in NEB3 and NEB4 using dam− lambda DNA as substrate. Mutants with more activity than WT in NEB4 were selected as increased activity in NEB4 is an indicator of improved fidelity. The following mutants were found to have is more activity in NEB4: G075A, Q099A, G155A, and P022A/R90A. P154A NruI(P022A/R90A) is designated as NruI-HF.

4. Purification of NruI-HF

Two liters of cell ER2683(pUC19-NruI(P022AR90A), pACYC184-Sbo131M) were grown in LB with 100 μg/ml Amp and 33 μg/ml Cam at 37° C. overnight. The cells were harvested and sonicated in 20 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl. After a centrifugation at 15,000 rpm for 30 minutes, the supernatant was loaded on the 5 ml HiTrap™ Heparin HP column (GE Healthcare, now Pfizer, Inc., Piscataway, N.J.) pre-balanced by the same buffer by syringe injection. The column was then loaded on the system by the following procedure: 48 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl, 100 ml 10 mM Tris-HCl, pH 7.5, 50 mM-1M NaCl linear gradient and followed by a 10 ml 10 mM Tris-HCl, pH 7.5, 1M NaCl step. The eluted fractions were then tested for activity. The fractions with highest activity were further concentrated by Vivaspin® 15R (Vivascience, now Sartorius Vivascience GmbH, Goettingen, Germany). The concentrated NruI-HF was then added an equal volume of glycerol and stored at −20° C.

5. Comparison of NruI-HF and NruI-WT

The FIs of NruI-HF and NruI-WT have been determined separately on dam− lambda DNA in four NEB buffers with diluent A. The result is listed in Table 32 (below).

TABLE 32 Comparison of NruI-HF and NruI-WT NruI-HF NruI-WT Improvement Buffer Activity FI Activity FI Factor NEB1 0.4% ≧64 12.5% 64 ≧1 NEB2 6.3% ≧1000  50% 250 ≧4 NEB3 6.3% ≧1000  100% 500 ≧2 NEB4 100%  ≧16000 12.5% 32 ≧32

NruI-HF performed best in NEB4, in which the FI was ≧16000; NruI-WT performed best in NEB3, in which the FI was 500. The overall improvement factor is ≧16000/500=≧32.

Example 32 Engineering of High Fidelity NspI 1. Expression of NspI

NspI was expressed in E. coli transformed with pUC19-NspIR and pACYC-FatIM, each contains NspI endonuclease and methylase gene. The cells were grown at 37° C. overnight in LB with Amp and Cam.

2. Mutagenesis of NspI-HF

All residues Cys, Asp, Glu, Gly, His, Lys, Asn, Pro, Gln, Arg, Ser, Thr were changed to Ala at positions 9, 10, 12, 13, 14, 16, 17, 18, 19, 20, 21, 23, 26, 29, 30, 31, 32, 34, 36, 37, 39, 40, 41, 42, 44, 45, 46, 47, 50, 51, 52, 53, 55, 56, 58, 59, 60, 61, 62, 63, 64, 65, 66, 70, 71, 72, 73, 74, 77, 78, 80, 81, 82, 83, 85, 86, 87, 89, 90, 91, 93, 94, 96, 97, 99, 100, 102, 104, 107, 108, 111, 114, 116, 117, 120, 121, 122, 123, 124, 125, 126, 127, 128, 132, 133, 134, 136, 138, 139, 141, 143, 144, 145, 146, 147, 149, 150, 152, 153, 154, 155, 157, 158, 159, 161, 164, 165, 166, 167, 168, 169, 170, 171, 172, 175, 176, 177, 178, 180, 181, 184, 185, 186, 187, 188, 189, 191, 193, 195, 199, 200, 201, 202, 203, 205, 206, 208, 209, 210, 211, 212, 213, 215, 216, 217, 220, 222, 225, 227, 230, 231, 234, 235, 236, and 238; Tyr was changed to Phe at the positions of 48, 75, 113, 115, 198, and 224.

The mutagenesis methods were inverse PCR with paired primers is followed by DpnI digestion. The treated product was then transformed into E. coli strain ER2566.

3. Selection of NspI-HF

Selection of NspI-HF was achieved using comparison of activity in NEB3 and NEB4 using pBR322 DNA as substrate. Mutants with more activity than WT in NEB4 were selected as increased activity in NEB4 is an indicator of improved fidelity. The following mutants were found to have more activity in NEB4: S097A and E125A. NspI(S097A) is designated as NspI-HF.

4. Purification of NspI-HF

Two liters of cell ER2566(pUC19-NspI(S097A), pACYC-FatIM)) were grown in LB with 100 μg/ml Amp and 33 μg/ml Cam at 37° C. overnight. The cells were harvested and sonicated in 20 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl. After a centrifugation at 15,000 rpm for 30 minutes, the supernatant was loaded on the 5 ml HiTrap™ Heparin HP column (GE Healthcare, now Pfizer, Inc., Piscataway, N.J.) pre-balanced by the same buffer by syringe injection. The column was then loaded on the system by the following procedure: 48 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl, 100 ml 10 mM Tris-HCl, pH 7.5, 50 mM-1M NaCl linear gradient and followed by a 10 ml 10 mM Tris-HCl, pH 7.5, 1M NaCl step. The eluted fractions were then tested for activity. The fractions with highest activity were further concentrated by Vivaspin® 15R (Vivascience, now Sartorius Vivascience GmbH, Goettingen, Germany). The concentrated NspI-HF was then added an equal volume of glycerol and stored at −20° C.

5. Comparison of NspI-HF and NspI-WT

The FIs of NspI-HF and NspI-WT have been determined separately on pUC19 DNA in four NEB buffers with diluent A with BSA. The comparison is shown in FIG. 16, and the result is listed in Table 33 (below).

TABLE 33 Comparison of NspI-HF and NspI-WT NspI-HF NspI-WT Improvement Buffer Activity FI Activity FI Factor NEB1 100% ≧4000 100% 250 ≧16 NEB2 100% ≧500 100% 16 ≧32 NEB3 12.5%  ≧250  25% 120 ≧50 NEB4 100% 500  50% 32 ≧16

NspI-HF performed best in NEB1 and NEB4, in which the best FI was ≧4000; WT NspI performed best in NEB1 and NEB2, in which the best FI was 250. The overall improvement factor is ≧4000/250=≧16.

Example 33 Engineering of HF BsrFI 1. Expression of BsrFI

BsrFI was expressed in E. coli transformed with pBAD-BsrFIR and pSYX33-HpaIIM, each contains BsrFI endonuclease and methylase gene. The cells were grown at 37° C. overnight in LB with Amp and Kan with arabinose induction.

2. Mutagenesis of BsrFI-HF

All residues Cys, Asp, Glu, Gly, His, Lys, Asn, Pro, Gln, Arg, Ser, Thr were changed to Ala at positions 7, 8, 9, 12, 13, 15, 16, 17, 18, 19, 20, 21, 23, 25, 26, 28, 32, 35, 36, 37, 39, 40, 41, 42, 44, 45, 46, 48, 49, 51, 52, 56, 59, 61, 62, 64, 65, 66, 68, 72, 73, 74, 75, 76, 77, 80, 86, 87, 89, 91, 93, 94, 95, 97, 98, 103, 105, 106, 108, 109, 111, 113, 114, 117, 118, 119, 120, 121, 122, 123, 126, 128, 129, 130, 133, 134, 135, 136, 137, 139, 142, 143, 144, 145, 146, 151, 152, 153, 154, 157, 158, 159, 161, 162, 163, 165, 166, 168, 169, 170, 171, 173, 174, 177, 180, 181, 183, 184, 185, 187, 189, 190, 194, 196, 198, 199, 200, 202, 203, 204, 205, 206, 208, 211, 212, 213, 214, 217, 218, 222, 224, 226, 229, 230, 231, 233, 235, 238, 240, 241, 242, 243, 245, 246, 248, 249, 250, 253, 254, 257, 258, 259, 262, 264, 265, 266, 267, 268, 269, 272, 273, 276, 278, 279, 281, 282, 284, and 285; Tyr is changed to Phe at the positions of 14, 34, 53, 90, 96, 99, 125, 160, 227, 236, 237.

The mutagenesis methods were inverse PCR with paired primers followed by DpnI digestion. The treated product was then transformed into E. coli strain ER2566.

3. Selection of BsrFI-HF

Selection of BsrFI-HF was achieved using comparison of activity in NEB3 and NEB4 using pBR322 DNA as substrate. Mutants with more activity than WT in NEB4 were selected as increased activity in NEB4 is an indicator of improved fidelity. The following mutants were found to have more activity in NEB4: K021A/I031R and T120A. BsrFI(K021A/I031R) is designated as BsrFI-HF.

4. Purification of BsrFI-HF

Two liters of cell ER2566(pBAD-BsrFI(K021A/I031R), pSYX33-HpaIIM) were grown in LB with 100 μg/ml Amp and 33 μg/ml Kan at 37° C. overnight with 0.2% arabinose induction after 8 hours. The cells were harvested and sonicated in 20 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl. After a centrifugation at 15,000 rpm for 30 minutes, the supernatant was loaded on the 5 ml HiTrap™ Heparin HP column (GE Healthcare, now Pfizer, Inc., Piscataway, N.J.) pre-balanced by the same buffer by syringe injection. The column was then loaded on the system by the following procedure: 48 ml 10 mM Tris-HCl, pH 7.5, 50 mM NaCl, 100 ml 10 mM Tris-HCl, pH 7.5, 50 mM-1M NaCl linear gradient and followed by a 10 ml 10 mM Tris-HCl, pH 7.5, 1M NaCl step. The eluted fractions were then tested for activity. The fractions with highest activity were further concentrated by Vivaspin® 15R (Vivascience, now Sartorius Vivascience GmbH, Goettingen, Germany). The concentrated BsrFI-HF was then added an equal volume of glycerol and stored at −20° C.

5. Comparison of BsrFI-HF and WT BsrFI

The FIs of BsrFI-HF and BsrFI-WT have been determined separately on pBR322 DNA in four NEB buffers with diluent A. The comparison is shown in FIG. 17, and the result is listed in Table 35 (below).

TABLE 35 Comparison of BsrFI-HF and BsrFI-WT BsrFI-HF BsrFI-WT Improvement Buffer Activity FI Activity FI Factor NEB1 100% ≧500 25% 16 ≧32 NEB2 12.5%   ≧64 100%  4 ≧500 NEB3 NC NC 3.1%  8 ≧−8 NEB4 100% ≧500 50% 16 ≧32

BsrFI-HF performed best in NEB1 and NEB4, in which the FI was ≧500; BsrFI-WT performed best in NEB2, in which the FI was 4. The overall improvement factor is ≧500/4=≧120.

Example 34 Engineering of HF BspEI 1. Expression of BspEI (SEQ ID No. 34)

BspEI was expressed in E. coli transformed with pLazz1-BspEIR and pACYC184-BspEIM, each contains BspEI endonuclease and methylase gene. The cells were grown at 37° C. overnight in LB with Amp and Cam.

2. Mutagenesis of BspEI-HF

All residues Cys, Asp, Glu, Gly, His, Lys, Asn, Pro, Gln, Arg, Ser, Thr were changed to Ala at positions 7, 8, 10, 11, 12, 13, 14, 17, 19, 20, 21, 22, 23, 27, 30, 31, 33, 34, 35, 36, 37, 39, 42, 43, 44, 45, 46, 48, 49, 51, 52, 53, 54, 55, 56, 58, 59, 60, 62, 63, 64, 66, 67, 68, 71, 72, 73, 74, 75, 78, 79, 81, 82, 84, 85, 88, 89, 91, 92, 93, 94, 95, 96, 98, 101, 102, 103, 106, 107, 108, 110, 111, 113, 114, 115, 117, 121, 122, 124, 126, 127, 128, 129, 132, 133, 135, 136, 137, 138, 140, 141, 148, 149, 151, 153, 155, 156, 157, 160, 162, 164, 166, 167, 168, 169, 172, 174, 175, 176, 177, 178, 182, 183, 184, 185, 186, 187, 189, 192, 193, 195, 196, 197, 198, 199, 200, 201, 203, 204, 208, 209, 212, 213, 214, 216, 217, 218, 219, 221, 222, 228, 229, 231, 232, 233, 234, 235, 236, 237, 238, 239, 240, 242, 244, 245, 246, 250, 251, 253, 254, 255, 256, 258, 260, 261, 263, 264, 266, 267, 269, 270, 271, 272, 273, 275, 276, 277, 281, 282, 283, 285, 286, 288, 289, 293, 294.

The mutagenesis methods were inverse PCR with paired primers followed by DpnI digestion. The treated product was then transformed into E. coli strain ER3081.

3. Selection of BspEI-HF

Selection of BspEI-HF was achieved using comparison of activity in NEB3 and NEB4 using unmethylated lambda (λ⁻) DNA as substrate. WT BspEI has more activity in NEB3, the one with more activity in NEB4 were selected. 6 mutants are found to have more activity in NEB4: K7A, T10A, N11A, N14A, Q232A and T199A. T199A has much higher activity than WT in NEB4. BspEI(T199A) is designated as BspEI-HF.

Example 35 Engineering of High Fidelity BamHI (Additional Mutants)

BamHI (SEQ ID No. 35) recognizes and digests at G/GATCC as described in Example 1 of International Publication No. WO 2009/009797. A mutant BamHI(E163A/E167T) was selected as the high fidelity version of the BamHI.

A complete coverage of mutation was done on BamHI. Aside from the residues reported in the previous patents and applications, the rest of the residues were also mutated to Ala at position of 3, 7, 8, 15, 16, 21, 22, 23, 24, 27, 29, 31, 33, 34, 35, 37, 38, 39, 45, 47, 48, 49, 53, 54, 55, 56, 57, 58, 59, 60, 63, 64, 67, 68, 73, 74, 79, 80, 82, 83, 85, 90, 91, 92, 93, 95, 99, 100, 102, 105, 108, 109, 110, 112, 115, 116, 117, 124, 125, 127, 128, 129, 130, 131, 134, 136, 138, 140, 141, 142, 143, 144, 145, 147, 148, 151, 152, 156, 158, 159, 162, 164, 166, 168, 171, 172, 173, 174, 175, 176, 177, 178, 179, 180, 185, 187, 188, 189, 190, 191, 192, 194, 197, 198, 203, 206, 210 and 212.

Among these mutants, P92A, P144A, G197A and M198A have higher fidelity than the wild type BamHI. P92A can be an alternative high fidelity BamHI. 

What is claimed is: 1-74. (canceled)
 75. A method of identifying a fidelity index (FI) of a restriction endonuclease and one or more variants thereof; comprising: selecting a reaction buffer and a DNA substrate containing the binding and cleavage site of the restriction endonuclease; permitting serially dilutions of the restriction endonuclease and the one or more variants thereof to cleave the DNA substrate; and determining an FI for each of the restriction endonuclease and the one or more variants thereof.
 76. A method according to claim 75, further comprising: comparing the FI for the restriction endonuclease to the F1 for a variant thereof to obtain an improvement factor for the variant.
 77. A method according to claim 76, wherein the improvement factor is greater than
 2. 78. A method according to claim 75, wherein the reaction buffer comprises potassium acetate, Tris acetate and magnesium acetate; or magnesium chloride. 